$600 could get you a Leupold 30x40 FX-III, Sightron 6.5-20x50 SII Big Sky or 36x42 SII Big Sky, the weavers mentioned before, a few of the Nikon Monarchs, Bushnell Elite 4200 in 6-24 or 8-32, along with a few more nice options.
The question really comes down to what you want to do with the rifle. When it comes to long range shooting some people shoot amazing groups with only a 20x scope. Then again others bump up to 50x and never come down from that. I personally don't see the point in a paper punching long range scope that is anything-20x magnification. You will never dial below 20x when shooting long range. When mirage gets thick people tend to back down to mid 20s-low 30s. Others stay at 40-50x. If you think this scope will ever go on a hunting rifle then something in say 6.5-20 will be a decent dual purpose scope. Still that said if all you are doing is say shooting at 1000 yards why would you bother with something that only goes from 6.5 that you will NEVER use to 20x which is on the low end of the spectrum? Some people don't like fixed zoom scopes as they just can't shoot well with heavy mirage and high magnification. Even then there are a few decent 8-32 or 34x scopes out there in your price range that I think will be much better long range PAPER punching scopes.
The question really comes down to what you want to do with the rifle. When it comes to long range shooting some people shoot amazing groups with only a 20x scope. Then again others bump up to 50x and never come down from that. I personally don't see the point in a paper punching long range scope that is anything-20x magnification. You will never dial below 20x when shooting long range. When mirage gets thick people tend to back down to mid 20s-low 30s. Others stay at 40-50x. If you think this scope will ever go on a hunting rifle then something in say 6.5-20 will be a decent dual purpose scope. Still that said if all you are doing is say shooting at 1000 yards why would you bother with something that only goes from 6.5 that you will NEVER use to 20x which is on the low end of the spectrum? Some people don't like fixed zoom scopes as they just can't shoot well with heavy mirage and high magnification. Even then there are a few decent 8-32 or 34x scopes out there in your price range that I think will be much better long range PAPER punching scopes.