If it were me, I'd get a Peavey Ultra Plus used off of eBay. It should be $350-400. Three channels, very good clean, and the precursor to the 5150 (ver 1) overdrive channel. With the extra money, I'd get a choke, output transformer and adjustable bias knob to add to it. It'd be about 500, maybe a little more, but you could spread out the parts upgrades to ease the blow. Of course you'd need the cab, but you might be able to find an avatar 2x12 on craigslist cheap. It is a very versatile amp. Spring Reverb, Effects loop, multi eq for the channels. I keep waiting for one to be a steal, just to grab one.
Patrick