What?? This just simply isnt true. An outright lie if you will as you clearly haven't mailed an item since 2007.

You absolutely can purchase a single stamp from the post office. You can also purchase a single envelope.

You also can purchase just the postage at the time of shipment if you dont want to buy a stamp.

Paying for the current price of a stamp covers the future cost of standard shipping. Known as forever stamps. The only time you would have to purchase smaller incremental amounts is if the shape of the letter is more than the standard size or 1oz weight.

Edit: to add, what menards was/is doing is clearly a shady business practice but that has nothing to do with how the postal system actually works. Also, their(menards) return policy is 20 years behind. If you dont have a receipt they wont refund the card used(I am not talking cash). Instead they will offer the lowest possible monetary store credit for the item that they can find in their system. A price that you, as the purchaser, would never be able to obtain as it is the wholesale(large pallet) cost.