I really, really like the 3" Home Depot foam. I quit sleeping on the ground about 5 years ago until I built my first pad last year. 15 nights on the ground last year and 11 this year.
I bought some of the firm eBay foam that Altaholics posted and it seems quite similar in density to the HD foam.
Caveat Emptor/you get what you pay for/etc, I do understand that the Home Depot foam doesn't have the longevity of more expensive foams. I don't intend to roll my pads much. My 3" pads went on the Main last year and never got rolled--they were transported flat, flat as seats in the raft, and slept on flat. I store them flat.
I may or may not get 20 seasons at 40 nights a season out of it, and if it mysteriously goes flat in 5 years, I'll post up here and admit it.
I now have (5) pads: (2) x 3" HD foam, (1) x 3" eBay foam, and (2) x 2" fabric store foam. I can outfit my entire family and I have $175 in ALL of them, plus a $16 silicon roller. I already had the heat gun. If the Home Depot foam goes flat, I'll slit the pad and replace the foam. Pretty sure I'll get my $25 worth out of it before that happens. For as good as I've slept over the past two seasons, I've already got my $25 worth!!
This can be an expensive sport. I'll spend money where necessary, but I feel this is a place that I can cut costs.
Everyone gets to make their own decision on that price point!