I use an EWD with a Garmin 12XL all connected to an IPAQ HX4700 PDA using a cable provided for this purpose by Severn Valley sailplanes. I run free LK8000 software on the PDA. The IPAQ cost me about £50 on ebay, there are usually plenty on there.
If you use an EW micorecorder you can also get a suitable cable from Severn Valley I believe and then you do not need a seperate GPS.
The cable I use also includes a 12V to 5V converter to run the IPAQ from the glider batteries.