I did see Burpee seeds for $1.49 at Lowes, but wasn't much in term of heirloom
For regular vegetable seeds, ---------and I know this is going to be controversial because there is a big thread bashing this gardener because of his supposed '87yo' tomato seeds---------, I now only buy from
MiGardener. His seeds are good quality and very generous amount all for 99cents. You get double amount of seeds compared to a regular package.
Can't help with regular potatoes, but for sweet potatoes there is
Sandhill Preservation Center with reasonable pricing, but you have to order by mail.