Did you look at non ATI brand radeon 9800's? Sapphire makes some affordable ATI cards. An oem sapphire 9800 pro should be pretty close to your budget.
For video editing, ATI card is pretty much one of the best you can find. The hardware MPEG decoding quality is very good. The 2D quality is excellent as well. That's the main reason why I got an ATI card myself
The radeon 9600 pro and 9800se aren't bad either, reasonably cheap and very good quality/performance.