You might try calling around to Radio Shacks near and far to see
if they might have one available as discontinued/marked down/open package.
That's exactly what I did last September, and found one for $7.99 at an RS store near to me.
Amazingly, I see the same one posted by someone (not me) right now on our local craigslist for $10.
It programs several Radio Shack and GRE scanners that I have (the PSR-310 for one),
along with my Yaesu and Kenwood amateur radios (with plug adapted).
Alternatively, with very, very basic electronic experience,
you can build your own quite easily.
The plug's pin-outs are on the web.
You also could
modify one of the super cheap programming cables
used for most of the Chinese ham handhelds, too.
Just say NO to high priced cables.