Some recent serious games auctions on eBay:

Serious Sam Collection Microsoft Xbox 360 *Factory Sealed! *Free Shipping!

$14.95
End Date: Friday Feb-16-2018 17:57:00 PST
Buy It Now for only: $14.95
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Serious Sam HD: The Second Encounter - PC
$6.97
End Date: Sunday Feb-18-2018 11:37:07 PST
Buy It Now for only: $6.97
Buy It Now | Add to watch list