The $350 is a fair price as most dealerships around here want anywhere from $600-$850 to do the work. The aluminum Lim gaskets are on the 04+ supercharged engines. The gaskets can be had for around $45, but most dealerships will mark them up considerably. I needed a set once and had to pay $85 at one of my local stealerships.
Make sure they drain your oil after their done, otherwise you can spin a bearing on your engine. I would run synthetic afterwards as theirs less chance of spinning a bearing because the water/oil is less likely to seperate. Make sure they replace the plastic coolant elbows as well as the supercharger coolant o-rings (2 of them).
Goodluck
