In the last decade I spent a fair bit of time working on the idea of buying and refurbing Missile site. I researched Atlas, Titan and Nike sites and even joined a list of ex-air force missileers. One thing about those guys who spent years in them- they talked a lot about the hazardous chemicals, and when one of these sites would come onto the market often people who had worked there would talk about accidents that had happened and various dangers.

To be explicit: What the Air Force considered "Safe" for a situation in which the guys in the station are a long way away in a control room, and what you might consider safe for your house or work environment are very different. The fuel refilling area, where there was a massive spill that wasn't really cleaned up, might be your living room, if you did a conversion. Not saying it's not safe, just be aware and if you go into this, find some guys who served there and get their info.

The TLDR of my years looking into this:
0. Nikes were first and are little more than garages with opening roofs. Not too exciting. Atlas was the next generation and these have buried silos and control rooms, there were several models with the Atlas -F probably the most interesting. Titan is the Big Kahuna of them. They have miles of tunnels and usually multiple silos (I think they cam in 3, 6 and 9 configurations) and massive power rooms and control rooms and all kinds of stuff.

1. The people selling them have dollar signs in their eyes, much of the time. One Titan site I ran down the history of (I doxxed the owners effectively) was bought for $30k in the early 1980s, has never been listed for less than $1M, has never sold, and most recently was listed for $3M. This despite a massive hole in the power station wall, which alone will cost $300k to fix, probably. Most of these are absurdly priced. Realistically, it doesn't matter if the government spent $300M building it, an unrenovated site should cost maybe $100k more than the land itself. The cost of renovation will be more than the cost of getting an equivalent housing built from scratch by a "survivalist" oriented builder, in most cases.

2. If it's not renovated it's going to cost you a lot to renovate. IF that Titan site had been renovated (like some of the homes in Kansas) then maybe it would be worth $3M But renovations to make something like this livable, extremely expensive, and problematic because who wants the liability of making a home out of a toxic waste site (the silos in Denver area are sold with an attachment declaring them such, and I think forbidding living in them.)

2a. If you don't have $300k (atlas maybe) - $1M (titan, minimum) for renovations you may not be ready for this. (There is a couple near Kansas City that renovated an Atlas, probably for a lot less, and they used to give tours.)

3. The best place to go is probably here, if you're serious: http://www.missilebases.com

4. The same sites come up for sale, over and over again, over many years (see #1) They aren't building any more but they aren't running out of them. Supply remains pretty constant.

An anecdote: I discovered the owners of the Titan site I wanted were real estate pros in California, and was hoping they were really leveraged. This was during the bubble (which having studied economics I knew would collapse) I was hoping they'd be desperate to sell their site after the bubble collapsed and after we were more than 5 years away from 2001 (and the survivalist surge that happened right after). Alas I was wrong, their prices went up. Since the crash their prices have come down a bit, but they're still 10x where it makes sense.