The first step is to get a proper diagnosis. I'm not saying you're wrong, but it would be an uncommon failure for that transmission.
My best suggestion is to join the forum at
http://forum.ih8mud.com/60-series-wagons/ and ask questions there and try to find a knowledgeable and reputable mechanic in your area that can do the work or help you find what you need.
Price will vary dramatically depending on what is actually needed and who you are paying to do the work. Good luck. FJ62s are great rigs.