The gasket is integrated into the cover, but it shouldn't have to be replaced. The main concern while removing the valve cover (to the best of my knowledge) is making sure you don't strip the allen bolts that secure it.
I have 2 TDI's that have had 4 TB changes total, never had to replace the valve cover.
WRT the cost of "repair":
The parts are ~$350 at DieselGeek
. That doesn't include the valve cover, but for good reason.
Several TB gurus on this board would be happy to do it for you for ~$250 labor. So you'd save close to $500 and it would be done right.
Where are you located?