First let me correct myself. In my previous post, I mispoke and referenced rear main bearing. This is not the correct part. What I meant to say was the rear main seal. The rear main seal only costs about $14 at the parts store.
Yes, changing the rear main is a major job. Several ways to do it like removing the tranny or pulling the engine so you can get to the seal. the seal is easy to remove and install, all the time and effort is spent getting to it. Basically, its the seal at the rear end of your engine's crankshaft. When this seal breaks down, oil will leak into your tranny bell housing and drip out the grommet or the access plate.