How much depends on a few things including if you are going to use used parts, scrap yard parts, or a doner car. You also have to switch out the CPU and a few parts off the engine which support vacume tubes and electronics. Possibly the drive shaft, the clutch and of course adding the clutch pedal.
On the one side, how long can you be with out your car and how much money can you spend on parts.
On the other side, how much is your car worth verses how much the next car will cost you. You can find some real deals out there.
Myself, I would go with a trade.
I love the manual trannies however I get stuck in so much stop and go traffic on the garden state I would have one leg like a muscle builder with in a year and walk in circles.