Not sure if there are Costco's near you, but can't beat their full synthetic offering of 10qt for $30. I believe it's made by the same company that makes Amazon's full synthetic, which tested as good as Mobile 1 and even better in some tests. (Mobile 1 at Costco on sale is nearly the same price, but for only 6qt so you'd have to initially buy two boxes since 4R requires 7qt per change).
I change my three vehicles' oil every 10K with full synthetic (all take 7qt each change). If you don't redline your engine frequently, 10K is still probably a very safe interval. I drive my 08 F150 with 250K mi very hard and it's done great at 10K intervals. (Most of the time I also replace one quart with Lucas Oil engine stabilizer*)
https://www.costco.com/kirkland-sign...100518855.html