Check out the Mesa F series amps. They can easily be found for $650 or less.
I used to have an F-100 that I used strictly as a pedal platform, and it's by far the best clean tone of any amp I've ever owned. The F series based on a Fender Bassman circuit. The lead channel isn't the best for high gain, but they can pull off some nice blues tones. The clean channel and reverb tank are fantastic though, especially for the price.