Does it have to be a valve amp, Bill? Unless you're opposed to them, you should be able to get a small rack-mount used S/S amp like a QSC, Crown, Peavey, Yamaha, etc., for that price. With the tube pre-amp, you'll still get that ole' valve magic, just without the power tube contribution. A MOSFET s/s amp will give you some of that back. Just my $0.02.
Cheers,
Kevin
FWIW, I use a hybrid (tube pre/ss amp) Eden bass head and my rack system is hybrid as well (F-2B and QSC). It's a nice compromise...sweetness of tube(s) and the extended range and rock-solid bottom that hi-current s/s provides in spades.