The issues is NAPA is geared towards supply garages and auto service places. They are not your typical retail supplier but more of a wholesale type distributor.
Yes they will sell retail, but there business plan and pricing structure makes them a bit more expensive than most other retailers.
I imagine they have tiered and preferred pricing levels.
If the NAPA is local to the OP and they truly do know he is a good local customer.
They should give him a cash account and offer him better pricing than just straight retail.
The garages that buy from NAPA regularly do not pay retail, but pay a discounted rate based on their sales volume.
The OP's loyalty should entitle him to a discounted rate.
But keep in mind if you shop strictly on price buy at the big box stores where price is king but finding a knowledgeable sales person and good service maybe a challenge.
On the other hand my local ACE hardware has great customer service and lots of help ,but they are always more expensive than Home Depot.
There is compromise involved a wise consumer will consider this when shopping and purchase accordingly. Finding the cheapest price should not always be the deciding factor.