lots of variables! I'm doing a 518 OD(46RH) in my 65 B. None of the OD trans were made to fit a big block so you have to "adapt" it. I'll be cutting off the stock bell and bolting on a J.W. Performance bell (about $290). You'll have to fabricate a new trans crossmember and shorten the driveshaft. You may also have to do some "clearancing" of the trans tunnel. Lots of other little things, like wiring the OD and lock up controls.
What you spend will depend on how tough you want the transmission to be and how much work you farm out.
My estimates run from $850 if I do everything myself, including a trans rebuild, to as much as $4000 if you just drop it off somewhere and tell em to have at it.