How would you get max value for this 93 Dodge van

It does start, transmission only goes in reverse now! When we parked it two years ago, it was only slipping bad, now only reverse.

I do know the early minivans (dodge-plymouth) had a problem with plugged up trans filters screwing up the transmissions. The garages would do a trans. flush by sucking it out the filler tube which would pull all the crap/dirt thru the filter and plug it up. They ruined many a trans. until they figured out what was causing it.