It's more expensive here but the price diff isn't that great between the big box stores & the local nurseries.
Local HD 9.75 / 3.0 cuft
Local nursery 12.75 / 3.8 cu ft (larger size)

I only need peat for the blueberry bed I'll be making since BB's are picky about pH & drainage ... the veggie bed won't have it.

Retail chains are able to sell items so cheap because of economies of scale - the more a store can buy, the less it costs and the less they can sell it for.

It's how Wal-Mart LIVES and is able to drive out their Ma & Pop competitors.

So I would support locals if you can afford it :)

I understand the economies of scale - but in the OP's example, isn't paying double at the garden stores a little beyond the pale? I often wonder if prices would come down if Big Box competition magically disappeared and garden centers and nurseries only competed with other garden centers and nurseries. Throw in the old fashioned hardware store for rakes and shovels and implements, etc.

I would always prefer to support locals, but sometimes pricing structure wins out.

Update: 12-7-2012

The price at Home Depot is $9.97 for 3 cubic feet.

Here is a link that might be useful: Peat Moss

Old thread, but: always look for sources that will sell bulk if you can. Bales are retail, which always means the highest price. You may find someone who bought more than they can use, and just want to get back some money right now.

This is good https://www.amazon.com/