Note that this isn't a PS3 for $299, it's a PS3 for $399 where you get a $100 gift card after purchase (meaning you can't use it on the PS3).
But as Matt said, Wal-Mart is a grocery store too (though their quality on fruit and veggies sucks) so it might as well be cash. Just make sure you're ready for a $399 hit in the wallet and not a $299.
Good find!