I have yet to receive my credit, but I ordered last Wednesday (5/19) during the brief period of time when RDR was $53.99 and the $20 credit was being offered.
Yesterday I found Excite Truck for Nintendo Wii for $30 at my local Sam's Club in Melbourne, FL. This is the cheapest price I've seen for the game. I'm not sure if this is a location specific thing or not, so YMMV.