Mine showed up yesterday. I'll have to think of something to do with that huge quantity since I'm an amateur and have only one car needing a polish! But considering it's $64.99 on AG, that Amazon deal of $11.99 was impossible to pass up.
Duragloss 503 (the gallon size of 501) is $11.99 on Amazon, with free shipping if you've got Prime or make an over $35 order. Seems like a price mistake to me, but I ordered a bottle.