I can't speak for the past since I just got a PS TV, but GameStop had P4G for $20 - $5 Kongregate coupon. Got a used copy last month for under $13 after taxes and PUR.
Curious to know if this rules out Hawaii too? We're not part of North America, but not quite considered international either since we're part of the USA.
Just FYI, the One Price Promise does have restrictions, so they do have an out if they don't want to apply it for RB2:
* May not apply to DVDs, CDs, video games, bundled offers, clearance or open box items
I had posted a link to these coupons earlier in the Smarty Pants for Wii thread before I got the email. But if I recall, you need to click the picture of the dad and kid to the left instead of the print coupons 'button'. Didn't make much sense.