Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
Did you need the instructions for the rear main seal?
Do you know the engine size?
Yes, unfortunatly the labor for the trans is about 7.4 hours, with an extra hour for the seal. Whereas the national average rate is about $75 per hour. Then there is the cost of the seal, abour $25 plus oil and filter, taxes and "shop fees".
It will normally go to the lowest point, (which seems to be the oil pan on that engine) about the middle of it in the rear.
Yes the trans has to come out to do the rear main seal.
If there are no problems with the crankshaft and the seal is installed correctly, there should not be any reasons for it to leak in the near future.
The only quick fix I know of would be some oil leak stopper, which normally swells the seals, but will eventually make them hard, and they need to be replaced anyhow.