I would have to go with Chris's suggestion for the Lee Enfield .303 No4. 4 inch groups with the iron sights at 200 yards is acheivable and with a 4x Scope fitted around 600 yards for again a 4 inch group. At 1000 yards with a bit more care taking into account windage should get you around 8 to 12 inch groups. It will also work in conditions where most other modern military rifles begin to fail. It is also very well balanced for handling making it easier/just as easy to handle than most military rifles despite being a few pounds heavier. I believe you can get them for a few hundred dollars in the US. Cheaper than a good air rifle and yet more lethal than something like an M16 or AR15.