That's pretty neat, Chad. Not a whole lot under the chassis when it doesn't have a power supply, eh? As to the price of 9-volts, dollar store or Big Lots type stores have off brands cheap which are fine for this purpose. And it's pretty easy to make a power supply for such a set and lots of room inside the cabinet for it. Looking around the electronic surplus places on line you can often find a 1:1 transformer (120 in/120 out) to build the B supply around. There were some like that with low voltage windings also a while back, for just a few bucks each. I bought some of these and used one to make a B supply and its 7 volt (open voltage) secondary was fine for three 6.3 volt heater tubes.
Edit: for example, I just found this dual primary transformer for $5.95 (I have no connection with this vendor.) It has two electrically separate primaries. One can be used for the input from 120VAC. The other primary can be the 120VAC secondary for your high voltage. The secondaries are two 10 VAC. They could be reduced in voltage and solid-state regulated for filament and bias. Would take a little experimentation but there are circuit diagrams out there that would be a basis to start.
http://www.alltronics.com/cgi-bin/it...ormer-DST-7-20