It sounds like at the bare minimum you will need to buy new case halves which are about $500 from the dealer. Your best bet is buy them off someone on here or eBay, but you need to be careful because lots of people have had the same problem that you have and try to pawn their garbage off on others. You may need a new counter chaft or shift shaft, gasket set, etc. and the price just goes up from there as you takit apart. If you post pictures, maybe we could help you more.
I am a bad judge of what people can do on their own mechanically speaking. I tend think people are capable of more than they actually are. Maybe you can get a friend to help you or something as paying a shop to fix your motor could cost over $1000 including parts. :thumbsup: