For your used stock trans, maybe $100 if it's local and someone wants it. They're all over the place around here. Shipping is insane and the nose cone would have to be removed in order for it to go by UPS. Too large and too common to bring any coin.
A real Freeway Flyer is more than just an R&P swap, and you certainly get what you pay for. Before I bought the swing axle for the Porsche, I checked everywhere and spoke with everyone, eventually I went with a builder out of Maryland if I remember correctly. If you want a trans built for hard high speed highway driving that will also live on the street and hold up to a decently built-up engine, you'll need to run four spyders, super dif, heavy side cover(s), welded gears and hardened keys MINIMUM. Plus the gears will need to be mixed and matched to keep the gap between third and fourth from becoming a dead zone. With a 3:88 R&P backed up against maybe a .77 fourth you'll need gears from the 411 in there to help with a good balance. With a box like this and a slightly taller tire, you'll be able to run-fast all night. As for over heating because of lower revs, the balance between the gears will take care of a LOT of that, plus the Freeway Flyer is meant to do just that, FLY ! ! Your revs will still be the same, the fan will still be moving as fast as before, but YOU'LL be moving MUCH quicker. With the increased speed, there will be increased air going into the engine compartment and through the remote oil cooler. If you aren't going to USE the trans for what it was built, don't bother.
If you've spent coin on the suspension and engine, don't just grab a "Freeway Flyer" and figure that a 3:88 R&P is gonna do it. That came stock in later Ghias and Supers, why spend real money on something that lame. Of course, as Alan mentioned, if the ride is done and together, leave it as is. Unless you like to go out hunting at night, a stocker is fine for both highway and local streets. Really.
I went through all of this with the 356 and the new Fiat, lots of options, lots of fine tuning in gear selection and such, lots of money spent, lots more to it than just a 3:88 R&P, but unless you really run a radical car or do some radical driving, there's no need.
Luck,
T