I own property in 2 states, Montana (with over 40 acres) and Southern Illinois (with 5 acres).
I have an interest in building a bunker on my property in Montana underground or at least partially.
This would be where I'd hold up if SHTF.
Ideally I'd like it to be able to hold 6 people comfortably. I already have a house there with my supplies/storage, so I can move this inside the bunker once built.
However, my question is, what's YOUR opinion on how much this would cost to build?

Prices vary wildly.

There are several companies who sell prefab shelters they'll deliver and bury for you and they range from $6,000 to $80,000 and more.

Having some contracting experience with roofing and decks and stuff I would estimate your DIY costs to be 40-60% the retail cost.

I guess it would depend if your going to do it yourself or hire a professional company. There are endless options either way. I suggest just doing a little internet research to see what appeals to you based on the amount you want to spend.

Well, if you build it at ground level you`d be prone to the entrance being filled up and you being trapped. If you do build, make sure the entrance is half a meter or so above ground level. On a hilltop you would be the best with a staircase to enter it. Then just fill back the top of the hilltop. Also, be sure that the door opens inwards. To many people have become snowed in with doors opening outwards and the door not being a 2-split door.

The most important part to a bunker is it`s entrance, as a bunker doesn`t leave you with multiple exits.

Air filtering system intake should also be far above ground, as well as a radio antenna for outwards communication. The same with optional solar panels.

For sanitation needs / toilet I would recommend an camping/burning toilet. In short, it burns your crap. Just be sure it has been properly tested and isn`t prone to catching on fire.

6 people would rule out a drybulk container. You`d have to go with sement I think, then some method of properly waterproofing it before filling it up on top of the hill. Sement also opens for making it dome-shaped inside. This would make the construct more solid and a bit more roomy. Heat would be trapped high up and cold air down, underground would keep it cool but not too cool, depending on walls and isolation.

Using the "sement tent" thing I saw on this forum once would be an idea you could work on.

When you build it consider the most important factors. Clean air, clean water, disposal system and/or water override system in case it starts leaking, heat and cooling, safety from outside elements and safety from being trapped inside.

What are you looking for? a fallout bunker or just a place to hold up for a bit while everyone is killing each other over food?

A fallout bunker will cost you some bucks. They have ones only that are all put togeather, all you have to do is dig a hole, drop them in and fill with dirt

Here's what you do. Ask around and find out who knows how to run a backhoe. If you're lucky you'll have a friend that can, or knows someone that can. Rent one for a weekend and dig yourself a big enough hole. Rent one of the packing machines that they use in road construction. Run that over the bottom parts of the hole. Find a cement company that will come over and pour cement for a floor. Make a thick and tall frame for it yourself. Now, hire a brick mason to build you a building in the hole, out of cinder blocks. After that you can build a roof on top of the blocks in the same way that wooden bridges are constructed. 12x2s stacked on end. I wouldn't go any longer than ten feet on the width unless you have a center support beam. Coat the roof with any thick and water proof paint. The thicker the better. Put tar paper over that. Put a thick door on it and make sure you have a tunnel arranged to get into it. The door is optional if you can get the majority of the tunnel underground and put a hatch on that. Now fill with dirt. Done, and it won't cost that much. Maybe a few grand.

Make sure it's got 4 feet of dirt over it, and some kind of waterproofing stuff that you would use on a basement.

I agree with the people who have posted on here. Now take all comments and put them in one and analyze them to get a good result in making your bunker. Id live in a bunker just because its low maintenance, safe, you don't have to compete with the neighbor with the best looking house and best and its well insulated.

There are a lot of things you will have to think about when DIY'ing a bunker. I think it's impossible to give you an estimate. It just really depends on what features you want. I've made several architectural drawings for clients of bunkers which give protection to nuclear attacks, viruses, a very large arsenal of # that can be thrown at you.
Lead plating, air conditioning, dirt, lose space, pressurized chambers and a lot more. The biggest issue I discovered was air filtration and conditioning. Especially with the minuscule dust that fry electronics, constipating the filters and tiny radiation parts from nuclear attacks.

Also the structural build of the bunker is very important. I used domes with several layers with regulated pressure for maximum strength, in stead of square rooms.

I can PM you the drawings if you like. Most of the structure was cast concrete with a lot of reinforcing with several layers and not bricks.

Make a hobo shed deep in the woods, it's much easier than digging a coffin. no ones going to go deep in the woods when SHTF except for survivalist woodsmen like myself.

You could do a simple 8'x20' steel bunker with an 8" concrete shell for around $10,000 - $15,000.

It all depends on how big you want to go. And what you want installed.

You would need to get a blast door.
You would need to get an NBC filter.
You would need ventilation.

Everything else is optional.
Food storage areas, plumbing, beds, etc.

I love it how we all suddenly becomes experts in the topic of discussion. If you are being serious why are you wasting time asking building/technical questions on a conspiracy forum? Did you think about contacting builders/engineers/suppliers?

First off define its usage short term on long term

Short term will be cheaper
Long term will be most expensive and considering your talking about 6 people and the space and logistics for them.

Air Filtration
Water Filtration
Heat and Cooling yes even underground those will be a problem for the simple fact people in a confined space will generate alot of heat and without a system to change out that heat and air it is as good as killing yourself.

The hygiene facilities bath's,showers, and water 6 people for however long you intend to hold up your will require some amount of space.

And yes It is a good idea to have room for supplies on hand that can not be touched by outside influence's.

A solid Door is a must if your talking about radiation protection remember time-distance-sheilding right angles to radiation dissipation at at least 1 entrance and 1 exist.

Main thing is how long you intend to hold up and have the supplies on hand for that duration and supplies to rebuild if there is such a thing.

A well stocked bunker isn't going to be cheap and the biggest thing that upset's me is see people cheaping out to save a buck that isn't going to save their live's.

And a bunker is a investment like no other that can be used for many things other than the end is nigh.

At least 100k to 250k for a well built and stocked shelter obviously your risking your life doing it any cheaper because there is no one person out that can tell you which shtf event is will end up being.

The best approach is a one size fit all or if you prefer a Zombie Apocalypse food water and shelter the survival triangle with the addition of clean air and clean water options.

my 2 cents.