They will install ONE, free, in your car if it didn't come with one. There'* a kit they have to order, and there'* a code they use to bill GM for it. I did it on my Bonneville. Before you do it, have a look at my links to see if you're okay with what they do to your car. You'll have to decide where to put it, either in the middle, or on one of the sides, or you might opt to pay for an additional one or two if you want more than one.
I had mine put in the middle, where my 2.5 year old'* car seat goes. The 4-month old goes next to him. In my wife'* 2001 Grand Prix GT, which came with anchors from the factory, she likes to put the kids on the sides, so the 2.5 year old won't mess with the 4 month old and wake him up.
Let me find the link where I did it, I think I had all the info including the part number and the GM service code for it. . . It'* in here somewhere.
Here you go. It was someone else'* thread, that I added to. They have the TSB number and everything. Scroll down for my photos of the thing installed.
97 SE, teflon wiper blades, Dunlop Sport A-2 tires, Leather steering wheel cover, Pioneer DEH-P480MP mp3 CDRW head unit, Pioneer 12-disc changer, iPod hookup, Boston Acoustic 3 way 6x9'*, Boston acoustic separates in door pods, Alpine 4 channel amp in trunk. Magnaflow dual outlet muffler and Ractive stainless tips. Autozone rice pipe and K&N 4750 intake kit. Clear corner lights. Energy Suspension end links.