Several major credit cards have a price protection policy for just this occasion, usually for 90 days. You just had to have paid for the item in full with that card and retained the receipt and a copy of the lower advertised price.
e.g...
I just applied the 8510 from Justin with a TL37 base (diluted half and half with water) and can confirm I saw exceptional coverage. I bought 3 gallons for ~400 sq ft and only really needed about 2 gallons (2 coats). I had so much extra I used it on a covered patio I didn't originally intend to...
I'm not sure I needed this, but thanks for the heads up. I had a $15.00 off eBay coupon I wouldn't have known about otherwise.
$14.95 shipped, plus ebates.