Oh, the good ole' days of audacity! I remember when I first began with it.. :-)
(On to Logic Studio, now.)
Well, the truth is that you can't get the greatest mic for $50..
If you saved up $100, then the Audio-Technica ATR2500-USB
would probably be your best route.
If not, then this Samson USB
might suit you!
I would recommend using them as room ambiance mics.
Best of luck!