The first thing you should do is get a repair manual & or video, &
then decide how you want & can afford to build this trans.
As for the cost, cant do it, don't know what your going to need,
but if you were to do just a simple rebuild/w bands, frictions, steels, & seals,
(master RBK & bands nothing extra) the cost would be significantly lower
then buying a new one, or one that has already been repaired,