In 1992, after reading through the owners' manual for my new Grand Am with the HO Quad 4, I decided to go with 5W-30 dino Pennzoil every 3 months whether it needed it or not, and to extend the same thing to my old 77 LUV. The only real change since then was in 02 when replaced the GA with a Cavalier with the Ecotec. Both have about 140K on them and warrenties are long gone. My wife drives the Cavalier 30 miles each way to work, mostly open 2 lanes. Some quarters the car see over 6000 miles. The truck gets mostly in town use seldom going more than 1/2 mile without a stop with occasional longer trips. This can't be too bad, the truck still holds good oil pressure, and the GA was doing fine at 180K and 10 years.
In 1992 the Pennz was less than a buck a quart and I could buy AC filters for $2.
Could I do better? If I get my AAP rebate, my last oil change would be about $24 for 10 quarts of oil and 2 Purolator filters including the L15436 cartridge for the Ecotec. I could live without the the thrill of the quarterly pouring in new oil. My goal is long engine life for only time and money needed.