Well, I know the parts total would be $100 is seals alone.

You dont have to remove the engine, just the trans and flex plate to replace the rear main seal. granted to remove the trans there are a couple other things to remove too.

When replacing the front seals (cam/front main) I would also change the Timing belt/tensioner while your at it, since you already had to remove everything else in the front. And if your water pump is questionable, R&R that too while your in there to save some money.

800 sounds about right. Dont hesitate to shop around.

But, I would do some troubleshooting myself first, before dropping a load of cash, Change the oil back to the blend, or clean the trans housing and look for leaks, remove the converter vents and feel for oil, spray the front down with bra-kleen and look for oil leaks to develop. But above all, replace and clean your flame trap first. Its cheap insurance.