> Anyone have any idea how much it should cost to have differential seals replaced and the bearing replaced... I have a quote for the AT part (rebuilding..) but the shop sends the diff out to someone else...,

I got a quote for $300 from German Transaxle in Oregon for a complete
rebuild of the final drive unit, so I definitely wouildn't pay much
more than that. It might not be much less than that either, though, as
changing the pinion bearing races requires removing the pinion shaft,
which requires pretty extensive disassembly.

> 
> Also, am I right in thinking that you have to remove the transmission to remove the diff???

Indeed. The final drive/differential unit is that 100 pound cast-iron
monster between the engine and transmission where the axles attach.
You have to separate the diff/tranny assembly from the engine and drop
it as a single unit, then separate the differential and transmission
later, after you drag it out from underneath.
 
On a side note, while the transmission is out is a good time to go
underneath there with a work light and inspect all those coolant hoses
you can't normally get at.