Doing a quick search on eBay, the cheapest auction on the first two pages was this:
04-2005-2006-2007-2008-2009 FORD RANGER TRANSPONDER KEY : eBay Motors (item 110466712328 end time Mar-06-10 0425 PST)
When I bought my '03, it only came with one key as well. But I didn't realize that the second key was inside a box under the dash that feeds the chip signal into the remote starter. I could have saved myself $50 if I took the dash apart BEFORE I went to the dealer to have it programmed.
If you've got a remote starter in the Ranger, there's a chance that the second key is under the steering column. Remove the knee panel and find the remote starter unit and follow it to another aftermarket box.