I do about 90% of my shooting at 500 yards or longer, and after twiddling with variable power scopes that I inevitably left at max power, I just bought a fixed power with good glass.
The USO shown above has their MOA reticle, 1/2 MOA knobs and EREK elevation. The whole thing was under $1200. They also make a 17x which is popular for longer ranges. Once you get into variables, the price skyrockets to around $2500.
Why pay so much? When you spend a lot of time looking at targets at 1000 yards you really start to appreciate the difference high end glass makes.
Since most people are worried about hitting a 20 inch gong at 1000 yards, it's a waste for them to spend that kind of money. The reality is, for most shooters it's a waste unless you happen to have money to burn or want bragging rights at the range.
If you can live with fixed power, you can start off with something like a SuperSniper from SWFA.com. It has a well deserved reputation with tactical shooters as a rugged scope with good optics. I can be had in 10x, 16x and 20x for about $300.