I bought my GEM used two years ago and did my training last spring in FL. After class I knew that I wanted to change over to a Shearwater display. The pocket book wouldn't allow it then. A buddy sold me his Shearwater and the research started. After calling around I found out that it was possible to save some money.

I ordered the Molex 4th cell assembly from Addhelium and the sensor housing cap from KISS. If you wanted to save even more you could use the cap from the Jetsam display. Simply unthread it from the sensor housing cap.
There are two downfalls but nothing major. The actual cable is longer than the Jetsam cable so you need to reroute it. I'm wrapping it around the CL hose a couple of time right now. Also the wire that has the Molex connector on it is long by a couple of inches. You just need to make sure that you get it stuffed in the cap far enough to not cause issues. I thought about seeing if I could get the pins out of the connector and shorten the wire that way. It's not worth it to me.