Hey guys, so my girlfriend and I are looking for a cheap, functional chastity device that will keep me secure and will not completely break the bank.
Check ebay and Amazon. There are many choices that are $30 or less. What works really well for one guy might be torture for another, since we are all built differently, so take reviews with a grain of salt.
Take measurements for your ring size. 45mm seems to be a common size. If you have time, it would be worth it to buy some sizing rings, because your concept of what "fits" will change a lot in the early stages.
Take measurements (morethan aa couple) of your flacid length. You don't want the cage to be longer than this measurement (a bit smaller is better for reasons that will be clear if you end up with a cage that is too big.)
I'd advise simple 2 piece steel designs (just a ring and a cage). There are some designs that are made of several pieces, and they are very difficult to put on without pinching.
Avoid plastic and run away from silicon.
Avoid hinged base rings unless you are thinking short term play only.
Other people may dispute some of the advice, because it really is down to personal preference.
Good luck.