The cost is usually under $500 on the 3.8L, but every shop is different. If you live near Dan Thurs, might see if it is a side job he would do. Dan may have done more 3,8L LIM gaskets in Wisc than 90% of GM dealer techs.
The issues with the LIM gasket replacement is not the quoted cost, but the risk of a shop getting into the job and then calling you up and saying you need this or that as they are doing the lIM gasket. At that point, you are a hostage. You may or may not need these things, but you will be charged a super premium for the additional parts and labor. A $500 LIM gasket can easily cost 3 times that, replacing stuff that may not truly need to be replaced, and they already have it off the car so it is a cash cow for them to charge you parts and labor for a part they already pulled. An example of this could be a heater hose.
2001 Bonneville SSEi, 219,000 miles.
Whats in my driveway:
1998 Chevy S10 4x4 ZR2, 1999 Olds Bravada, 2001 Pontiac Bonneville SSEi, 2007 Ford F-350 regular cab 2WD, 2008 BMW 335i coupe (Wife'* replacement for her Bonneville). The Bonneville is my favorite of all the cars in the driveway.