You can get "deals" on used trannies or even rebuilt ones.  But to get the job
done right so that you don't have to worry about it for the rest of the life
of the van why not spend the extra money to get somebody like Todd to overhaul
your trans for you and give you a warranty.
It is well worth the money when you consider the alternative may be your wife
with the baby, sitting on the side of the road late at night, waiting for
somebody to stop and call a tow truck.  If you are single or low on cash then
buy the cheap used transmissions and take your chances (I did when I was
younger).  But if you have the money then get it done right.  Trannies are not
something that you want to "cheap out" on if you can afford not to.
My 2 cents.
Ken Wilford
Van-Again
John 3:16