This is a question that comes up a lot, and it is worth repeating the link above and recommend reading it. It is one of the best, most comprehensive reviews of tactical scopes so far.
Long range shooting is impossible without good glass, but can be done without going bankrupt.
Vortex, Bushnell, Burris all have offerings that will get you in the game.
It bears repeating; get .1 mil turrets with a reticle subtended in mils. Even if you don't understand why now, when you get training it will.