Hi - Have you looked at the Flight1 GTN 750? http://www.flight1.com/products.asp?product=f1gtn The P3D one is $64.95, and well worth it, as it replicates nearly full functionality of the real unit, and can be placed into any aircraft, either as a 2D popup or integrated into the VC, as discussed here (required product registration to enter the GTN750 forum) http://www.simforums.com/forums/. It's GREAT!
Jim
http://www.mindstaraviation.com/The Mindstar GNS430/530 is a flight sim gauge that simulates 1 or 2 Garmin GNS430s or GNS530's (or a mix of 430 and 530) on your Flight Simulator panels. The software is compatible with the RealNav navigation database, available separately. It works with Microsoft Flight Simulator 2004, Microsoft Flight Simulator X, Microsoft ESP, and Lockheed-Martin's Prepar3D. It runs under XP and above.
Mindstar Aviation has both GNS530 and GNS430 available for $49.95.
http://www.mindstaraviation.com/
Unfortunately, RXP will not work in FSX:SE, or Prepar3D (any version). It is functionally "abandonware" in that Jean-Luc hasn't supported them for many, many years now.