Understood that VHF will be best bet. Again, just to show you how much I don't know, when reading online last night, I came across an article about encryption and my take away was encryption is something "civilians" are barred from using. The article was about some kind of Harris/L3 military handheld that sells for $1.5k-2k used and the author seemed to state that the only reason these were allowed to be sold was that the "encryption" had been removed/deactivated - I'm likely missing something it sounds like - I'm guessing it would have to do with the "strength" of the encryption?
Any answer we provide will depend on what country you are located in. Without knowing that, it's very difficult to give you accurate information. We don't care what city/state you are in, just the country.
Here in the USA, the FCC makes the rules, so most of the answers you will get are based off that. If you are located in a different country, all bets are off.
In the US, encryption is NOT illegal for civilians to use.
What you read about with the old military radios is called "De-mil" or Demilitarization, that is the remove the military specific modules of the radio. Since the US Military uses some different encryption modes that what others use, and there's no reason for them to be floating around out there in public, they are almost always removed before surplussing.
You can absolutely use encryption, but it depends on what radio service you plan on utilizing. Some radio services (amateur, MURS, FRS, GMRS, CB, etc) do not permit encryption in most cases, or any other way of hiding the meaning of the communications.
VHF is likely your best bet based on budget, but there are other options that will work. VHF Low band can work well in those environments. In some cases UHF can also.
Can I ask for a particular model that might fit the bill when you say used ones for around $300?
Before you go buying radios, there's some stuff you need to figure out.
Country you are in will have rules about licensing and access to certain frequencies. Doesn't matter what your use is, what your location is, or what your intents are, licensing of some type will be required in the USA, no exceptions.
Licensing will cost money. You need to figure out what radio service you are going to use before going any farther. Buying radios first is the wrong way to do this. Licensing first is the right way.
Once you have the licensing figured out, then start looking at radios. $300 per radio can be achievable IF you use either low tier Chinese radios or used commercial gear.
Recommending a specific brand/model will entirely depend on what your licensing is, what frequencies/bands you end up on, and what your exact needs are.
Most modern digital capable radios will do some level of encryption or scrambling. Purchasing used or Chinese low tier digital radios will get you something. But refer to the line above about -where- encryption is legal to use.
I also found something last night that is a bit more expensive, but it sounds VERY durable which has me thinking - BUT, it has encryption and I'm not sure I can buy it as a civilian? It was a Kirisun DP990 DMR.
Civilian or not doesn't have anything to do with it. Yes, you can buy it, but licensing still applies. Digital is legal in SOME radio services, but not all. Same with encryption, legal to use in SOME radio services.
But be careful buying the Chinese radios. Some are low tier junk that will give you problems. Kirisun seems to be one of the better brands, but you can really do better.
In addition to all this, you are going to need some way to program the radios. In most cases this won't be like a CB or FRS radio that comes pre-programmed out of the box. You'll need to program (or have the radios programmed) to the frequencies you are licensed for before you can use them. You can program them yourself, but it can be difficult and time consuming for those that don't have a background in communications. It's easy to make a mistake, and some mistakes can cause interference to other licensed users (even if you can't hear them), and that will lead to things you don't want.
So, before we get too far down this road:
-What country are you in?
-What is your technical background?
-What is your -real- budget?