I buy my 10W-30 oil at Wally World and use a well known HD "modern" brand name oil, and as I said above I add a small prescribed amount of zinc and phos. Based on purchasing 5 gallon containers, the total cost with small amount of additive is about $4.30 per quart; no shipping. As seen above, based on one's preferences one can spend up to almost double that per quart.
My 59AB rebuild has about 35,000 on it and has always used this oil. The engine doesn't have a filter, leaks a few drops out the bell housing hole, and the dip-stick level doesn't noticeably drop between oil changes.
Just my personal opinion and attitude, and I respect everyone's opinions and preferences .... maybe I'm lucky and should be "knocking-on-wood" with this engine, but if I'm changing the oil every 3,000 miles or minimum of once a year if less, and everything is going along okay, I prefer not to spend more.