I mean you can find any of these amps used in the $350'ish range.
Fender Hot Rod Deluxe (40 watt all tube, 1x12")
Vox AC15 (15 watts Class A tube, single 12")
Peavey Classic 30 (30 watts all tube, single 12")
All are great amplifiers for the money and all get quite loud.
Some off the wall suggestions would be some of fenders pawn shop series amps like the Fender Excelsior or Fender Vaporizer.. both are I believe 12-13 watt singe ended class A tube amps.