Smaller amp, bigger cab is the way to go for cheap tube power, big cabs are cheap cause unpopular, peavey 2x15 or two, an a sub 200w valve amp. Still be hard in that budget. Big cabs an the Bugera 1960 Marshall clone if you want the Lemmy sound might do you, but fairly specifically for that sound. Ashton BV300 is big power low budget, but isn't middly as it has a Fender type tone stack.
Best way to achieve goo sound on a budget is Sansamp VT bass an power amp, and no valves at all.