I agree with Marlin Man. What is Long Range to you!
400 to 600 you can get by with a 5.56/223 understanding the wind will significantly effect the round at those ranges.
600 - 1000 Although *not the optimum choice*, but the 308 would work since I have done many 1000 yard shots with the 308 (7.62X51)
Best Choices for 600-1000= 7 MM Rem Mag. and better yet the 300 Win Mag. or 338 Lapua. I love the 300 Win. Mag & *338 Lapua Mag for extended ranges!
The only issue with your request is the word "Cheap"! Larger calibers and specialty calibers are everything but cheap as well as the rifles. But you may want to also consider reloading for those calibers since it would also give you custom loads to match your rifle. Wind is one of the major considerations for any caliber shooting over 100 + yards. Good Optics are a must. And a 22 degree scope base mount if shooting the 308 Bolt Gun over 600 yards! You may want to do some ballistics and wind effect research on the calibers before making a final selection!
Good Luck with your choice!