FMS is a free D/L http://n.ethz.ch/student/mmoeller/fms/index_e.html

All you need is your transmitter and an interface cable that goes from your buddy box port to a serial or parellel port on the computer.

The cables are available on EBay for about $12 - $15 or you can make your own if you are handy. The FMS site has schematics for various setups.

This is a decent simulator, especially for the money.

Hope this helps.