Without knowing the history of the engine, I would say fair is 500-1K. Thats what I see them around here, anyway. Hell yeah its a cool option!!
Check out my 'burb thread to see my install on a 454. Having a complete truck would make it easier, IMO.
Dont know about the trans, but I've heard of this happening; possible shift linkage out of adjustment?? Seems too easy but one never knows.