I have an A2 fixed carry handle AR. The iron sights are fine for person sized groups at standard yardages. I'd like to add a removable mount (I tend to be tough on scopes) and some basic optics. The mounts range from $25 to $200 and I don't understand the difference. This is not a competition, 0.2 MOA shooting weapon, durability supersedes finite accuracy. Optics will probably be and old beat up fixed low power scope. Any guidance?