The part number for the hydraulic valve lifters in my car (and in many of our cars) is 17122490. I can get them for around $30 each.
I found information that says GM part number 12499225 is a package of 16 pieces of part number 17122490. The price on GMPartsDirect for 12499225 is $109. You get 16 lifters for a little more than the price of 3 if purchased individually.
I sent an email in to GMPartsDirect to confirm this, and will let you know how they respond. If this is true, it would be good information for our members.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)