Fender Rumble 500. Only about 300w with the combo, 500w with the extension cab. Light too.
Ashdown RM500 or the OriginAL C210T 300.
There's a few in the Amps For Sale section that look pretty good, the GR combo, or the MarkBass combo for example.
Though for that kind of money, you could pick up a good head & cab. Plenty of older, big heads available, or a few Class D's. That Laney Nexus 400 rig looks very tempting. There's an RM500 head & cab as well (but maybe a bit far to collect).