Is this too much money?

[SnS C10]

hey everyone i got a little problem with the truck. 84 silverado swb- stock 305 v8, 700r4.

Its got an oil leak. its coming from between the engine and the cover for the torque converter. i know this because i thoroughly cleaned the underside of the engine. I started it up and it started leaking on the back of the engine about where the oil filter goes. from there it goes down the TC cover and then on the exhaust. Now, its not the oil filter or lines, oil temp sending unit, or oil pan. So, that leaves the rear main seal right? I need this truck to get to work everyday so i took it to the shop and he said 350 to fix it plus an oil change, all new gaskets, seals, etc..Now im extemely mechanically inclined and would have no problem doing this, but he can have it done in one day and it would have a warranty. Does 350 sound like a good price? and is the seal just worn, or is there something else that could be wrong? thanks guys.