Try using an old Delorme Tripmate GPS
You need to modify the GPS unit to support NMEA, but anyone with a soldering Iron and 5 minutes of time can do this, and it works fine in Stumbler

Try checking out ebay.com or going to delorme.com direct. They sell refurbished Tripmates, complete for $50, Once you complete the modification, you are ready to roll

[More info on Tripmate and NetStumbler]
Follow the instructions here: http://wes.johnston.net/aprs/tripmate.htm


Happy Stumblin!