well this could be a learning experience for me too :P
it seems to me you could get a pci soundcard, and then two seperate pre-amps, a dual channel and a single channel.. there are some pretty inexepnsive ones out there, all together you could get 3 channels for your mics under 400, but not by much.., but you could end up with 2 different sounding preamps.. dunno if that would be a good thing or a bad thing.. i guess if you were happy with both sounds it would be good.
what i mean is you could get something like a
emu 0404 or a
M-audio delta 44
and then add the pre-amps, like a dual channel
m-audio audio buddy and a single channel like a
Studio Projects VTB1 or a
ART tube mp and then hook them up to the ins of the soundcard.
(now im not actually SUGGESTING this because i dont have any experience... but it seems to be a option. so anyone let me know if i got this idea right)