http://www.centrix-intl.com/ is a surplus/overstock place in Pasadena. They
have (now discontinued) Intel/Xircom USB->RS232 adapters for $1.99 each.
(you'll need a cable too, though.. probably another buck or two).
Click on the "Misc&Cables" item on the left hand menu, and scroll down a bit.
No idea if they will work with SDR software, etc, but they are certainly cheap.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
