Roy and Spearfish, i agree with the economy view, how old is your TX? and how much use has it had? if its lightly used i would convert, but if it's getting a bit worn new gear may be the way forward, i bought my Futaba T6's from ebay and spare receivers as well, also spares are readily available for ripmax, if you needed to replace sticks or switches, you can talk to them direct but only buy from a shop, they won't sell direct to you.
Regards the plug in board i don't know, are you in a club with an electronics man available, if not i could have a word with our guy, he converted my Robbe F14 navy to 2.4ghz without much trouble.
Regards
Mark