Primary arms has a great selection. Vortex has some good offerings but is a bit dated on some of them. Swampfox Optics has a new unit called the Raider that I may end up buying.

There are some other options, too. You can get a cheap prism from Monstrum to try it out and see if it agrees with your eyes. (Cheap as in $70-85 on sale.) if so, you an get a better one.

Fail fast, fail cheap.