I ordered one of these via the $99 MF blowout yesterday.
Apparently these amps are very well made and easy to modify. The grid leak resistor is as easy as soldering in a 1M resistor. http://www.thegearpage.net/board/sho...d.php?t=966529
Over here a guy sells a $56 kit (what it includes I don't know) that apparently replaces a few other components and gets good reviews. http://www.thegearpage.net/board/sho....php?t=1313375
I picked it up for a low-wattage guitar amp to test pedals with. But perhaps it'll work fine with bass, too. I'd expect bass to drive the input too hard, but I'm sure you could pad it down with a simple mod, or drop a lower gain tube into the preamps.
I figured for $99 you cannot even buy the raw parts to construct your own 5W amp so this would make a good platform to test / mod / learn on.