Why worry about the small difference in price per quart while the real issue is what oil will make OPs engine (a $4000 item)last the longest. Most of todays engines use 5W30 for year round application. We have posters who have used Walmart 5W30 and gotten 0ver 300,000 miles out of their engines without significant oil consumption.
I don’t see a $15 oil change at Walmart:
http://www.walmart.com/catalog/catalog.gsp?cat=495848
$24.00 Quaker State Pit Crew (includes lube, oil and filter - not a full express service package**)
$30.00 Standard Package (featured bulk oil or bottled oil, 5W20 included)
$40.00 High Mileage Package
$55.00 Synthetic Package (semi-synthetic blends or full synthetic)
$50.00 RV Package (featured oil, service available in select stores)
*Vehicles requiring more than 5 quarts of oil will require an additional charge.
**Available only with Quaker State Advanced Durability conventional motor oil 5W-20, 5W-30 and 10W-30 (using Ecoboxes only). Additional charge for more than 5 qts. Quaker State Higher Mileage Engine and Quaker State Ultimate Durability full synthetic not included. 2010 SOPUS Products. All rights reserved.