Dart to 4spd Conversion
Realistically, it will run around $3500+ if you can find a good trans that does not need rebuilt and do thrifty shopping. This is the way I did my Duster.
The cheapest way is to buy a parts car, and take everything off one car, but 4-speed parts cars are few and far between anymore. I got lucky for a 4-speed for my 70 challenger and bought a rust-bucket complete 4 speed car for parts, but then again, condition is unknown and more dollar will need to be spent for re-refurbishment of components, so I figure add another $1000 on top of the purchase price.