True, quality is an issue as well but that's a well-understood factor. 

The times I notice this is when it's the exact same brand, same type, just a different size. And the large economy size is often quite a bit more expensive, per unit cost, though everyone assumes it's cheaper.

Signal312

Frugal tip - the larger package is sometimes more expensive, per unit of weight

Its not just about price/lb though....lots of the generic brands can achieve that cheap price because its peanuts emulsified with palm/canola oil....(ie. there are less peanuts in the product).

All of life is a series of tradeoffs. You can be frugal with your peanut butter but may pay for it with your long-term health. 

I'm not particularly wound-up about peanut butter, and for occasional eating the health impacts of palm oil emulsion may not be significant. However, I'm simply pointing out the underlying concept: Its not just qty vs qty, but its quality-quantity vs quality-quantity.

 
