Even though I am the guy selling the 300T you are referring to, I will not be biased- try them all if you can. Some folks like others better than others. I have owned many a tube head so will give you my thoughts on some of the big tube jobs I'd look at in that price range or less:
Sunn/300T or Bassman Pro- I find the most versatile of the bunch. I thought the overdrive channel sounded like dirt until I started blending the clean channel in. The compressor is great on it as well but it took me a year of gigging to understand exactly how the strange controls worked (I had the Fender version for a few years in the early part of the decade). Again, versatile and can do just about any kind of tone you want but there are a ton of controls. As Jastacey said, be careful on the Sunn's and make sure it's been gone over. Mine hadn't, hence all the tech work I recently had done.
Peavey Classic 400- If you find one in good shape, jump on it. Versatile, much cheaper, built like a rock. Great drive channel. Overall it sounds like a Bassman (the classic kind) but beefier and louder than God.
Mesa Buster- My favorite clean sound ever. low amount of dirt compared to most tube heads and a little more modern sounding than the others. Nice lighter weight too. My second favorite after the 300T
SVT Classic- Pretty much a one trick pony at volume, but it that's the sound you want, nothing else comes close. For low volume settings, I really like the clean tone and find the EQ pretty flexible.
SVT II Pro_ I didn't like it as much as the others. It broke up too early, IMO, and I didn't like the graphic EQ.
I have never head the pleasure of playing through a Mesa 400 beyond screwing around with one in a store years ago but try one of those too. Same goes for a Peavey
VB-2 and Traynor YBA-200.
Listening to your band's myspace, it sounds like you use some effects on bass. I would also consider how well it takes pedals. Some amps just seem more pedal friendly than others