Sort of answered my own question: there are Samsung (aka Dell OEM) SSD on Ebay for about $400. I wonder if this would fit in the Blu-Ray/DVD slot?
http://cgi.ebay.ca/SAMSUNG-256GB-1-8...ht_6597wt_1137
Alternatively, perhaps I could replace my existing HDD with an SSD and then turn around and sell the 500Gb drive... or use it in place of the DVD drive? Or put it in a case and turn it into an external...?