Does anybody know the approximate cost for a mechanic to replace my intake gaskets?

depending on where you are, $400-$600 is about the going rate.

There have been reports on this site of owners being quoted over $1000 to do the job from the GM dealer. This problem has been ongoing for awhile and many independent garages are getting "well experienced" in doing these jobs, so to save a little money try going to non dealer repair shop to have the work done. Their prices tend to be a lot better and in some cases the quality of work too.

I just had the intake gasket replaced on my 97 Monte 3.1 last weekend. It was done by an independant mechanic. He also replaced the O2 sensor on the exhaust manifold, oil change, coolant flush and fill and replaced the little O ring aroung the "distributer" shaft. New starter too. This hunk of junk only has 54000 miles on it! $520.00.

ffgus,

Was that only for the upper intake gasket? My local shop wants $900 for a new intake manifold and upper and lower gaskets. My 3800,series II has 109,000 so I guess that isn't too bad that it lasted this long.

I replaced my own gaskets on a 3.1 with 95,000 miles. It's the lower one that leaks. Regular gaskets cost $50+, newer improved cost $80+.
It took me 10 hrs. because you have to remove everything on top of engine to get lower intake off, alt., pwr str pump, coil pack, ect.
You even have to remove valve covers, rocker arms, push rods because lower gasket goes around the push rods.
I notice lower gasket was not deteriorated as is claimed to happen on these engines. It was just leaking at rear corner. I would recommend trying to snug down 4 lower intake manifold "corner bolts", but they are hard to access unless you remove other parts.
With new gaskets, GM uses a higher torque value. By the way, it's a 10mm wrench/socket.