SWR Interstellar Overdrive has a built-in 5W tube power amp and dummy load in a 1U rack mount preamp. Maybe smaller (well, it's shorter but wider), but probably not cheaper now that they've reached vintage collector status.Ashdown has the CTM-15 with an internal load so you can xlr out to a power amp etc. I don’t think you could make a real tube power stage too much smaller than that (or much cheaper for that matter). I fact, I almost never run it alone.
I'm glad I got mine a while ago. I really like the UA in front of it. That, into a small solid-state amp and a couple of refurbished stereo speakers, has been my living room practice rig recently.
Ashdown also has (or had) the LB30n.2, which is 30W with a dummy load and speaker emulation. I heard a bass player using one of those on an outdoor stage with good PA (and a competent mix, no woofy subwoofers!) and it sounded amazing.
