I have a couple of HHB Radius 40s and have been quite pleased with them. I think I paid around $650 each, which is a bit more than your $ range, but each has a compressor and an equalizer as well as a pre-amp.
The Presonus MP-20 is also pretty good (~$450), but doesn't use valves (tubes) - it uses Jensen transformers, although the newer ones have transformers from a different source, and there's some question about how they sound compared to the earlier ones. I remember reading an article about how to retro-fit tranformers of the original type, which looked to be fairly straightforward (if you have skills with a soldering-iron), but I haven't bothered changing mine. The MP-20 has two channels, so that would fit in even better with your budget, but bear in mind the MP-20 is just a pre-amp, i.e. it doesn't have any equalizer or compressor.
As they say, "you pays yer money... you takes yer choice..."
Hope this helps -
- Wil