The GRE PSR-500 is the same as the Pro-106 except for the case design,
With that said, if you want to do proper scanning with digital, analog, trunked systems, etc, get you a Pro-106, which I think is well worth it at the sale price. I just picked one up my self this week. Great scanner and I learned how to program it, largely without the manual or the quick start guide (that got me started), very quickly.
While you are at radio shack, go ahead and pick up the USB programming cable. Online, you typically will be paying more (either from scannermaster or greamerica's site) for the cable, particularly when shipping cost is added in.