If you're computer savvy you can actually do this for under $60. Do a search here and via Google for RTL2832U. In a nutshell you'll need two RTL2832U dongles (R820T preferred), SDRSharp software which is free, the modified version of SDRSharp that is integrated with UniTrunker, DSD software which as you know is free, and a registered version of Virtual Audio Cable to transfer the unfiltered audio from the modified SDRSharp to UniTrunker...and finally of course, UniTrunker.
Or....one of the RTL2832U dongles and VAC would work fine to drive your PSR310.
Scott - Scan New England Webmaster
Radio Reference MA, RI, & CT Database Admin