There was a listing on ebay for the goodmark ones for $27 and change.Ha. Didn't see your post. How you getting them for 28 per set? Website showed $4 each.
I just checked a couple more sources. If you call your GM dealer, they should be able to get them through VPI. They only have 560 in stock. However, you cannot buy GM parts via retail through them any longer. You have to go through a GM parts dealer. Which sucks. So you have no idea what price you'll have to pay. Let us know how that goes.