Hi - if you want a GPS before going for JAA CPL, then FORGET IT! You won't be allowed to use it during your CPL training (or skill test for that matter), it's all dead-reckoning and position-fixing using navaids. You may want to develop these all-important skills during hour building, instead of just looking down the screen.
Don't misunderstand me, the GPS is one of the most amazing pieces of kit I've ever seen. On the other hand, I was once coming along with three mates on one of their hr-building flights in SA a while ago, and they navigated only by GPS, following the neat little line on the screen. OK, they logged the hours, but what they got out of that nav, practice-wise was... zilch!
Keep your money for some extra flight training - it always ends up costing more than you expected. The GPS can wait.
Cheers.