you
don't actually need a sound card for the server, only the client needs a
sound card.
How do you get the live audio on to the server without a sound card? By
streaming the audio data generated by a primary machine?
As for soundcards under $50, I guess eBay might yield an emu10k1 card, such as
the SBLive 512. That should be OK sound-quality-wise if we're talking about a
64k mp3/ogg stream.
Cheers
Daniel