Actually, all that I currently have (about 15-17 cans) was free. Home Depot had a thing going earlier this summer when you applied and was approved for one of their credit cards, they gave you a $25.00 credit for purchases.
They said that you could apply for up to 5 cards. I did the whole 5 and my wife did 3, all over the course of a few weeks. I used all that store credit to buy TruFuel.
I then closed each and every account while they all still had 0 purchases on them. My credit score took a slight hit, but cause of my excellent rating, it recovered quite quickly within a few months.
Home Depot's price per can was a little over $6.00 if I recall correctly.