This is NOT my auction, but I was perusing gunbroker.com, and found this auction for 18 20rd-ers at $15/ea. These have the alloy followers, seemed liked a pretty good deal to me. Seller was asking actual shipping cost, so that sounded pretty reasonable too.
20 Round Colt Mag Auction
Not bad I guess , but I can get a better deal ($10) in the EE from Magman on the same stuff.