i believe there are plenty of "cheap" practice amps
in the $300 range.......
new......
but i wouldn't want any of them, except strictly for a practice amp.
not a recording amp.
The really good low watt recording amps are going to be expensive.
A decent tube amp, even low watts, is going to be more expensive than $300 new......
the blues jr. is probably your best bet, but i doubt you'll find one in good condition for less than $250.......
but good luck searching.
if you want something that actually SOUNDS good, you'll have to cough up more dough.
and don't forget, a blues jr will get so friggin loud, that you wont be able to drive the power section very hard, and that's where the money is.........you could gig with that one, at the stage volume it puts out when it actually starts sounding sweet....
so you may want to consider a much lower wattage, 5 watts is plenty loud to record with, but no one makes a cheap one of those!
boogie used to make a 22 watter, class a, but they're not cheap!
do a search at harmony central.