I assume it's a velvet. I rebuilt mine for about $180 bucks but it was slipping. If yours is not slipping but is leaking then it is more then likely a seal, front or rear. If you can ID where it is leaking from you might get away cheap. IE if it is leaking from the rear you might be able to put a rear seal in without pulling the trans. If it is the front and you have some tools you can replace the front seal for pretty cheap.
Gone, out doing soft recreational past time with overpowered boat!