Bill, over the years I've had pretty good luck with Big A Tires. You've got a couple of outlets there in the Phoenix area, and I'd check with them. You might even be able to get a set of "blems" if you talk to the right guy. Blems have a cosmetic issue, but are not structurally compromised in any way. Have a look at WallyWorld, too. Once in awhile they will have a "deal." You could luck out.
I'd stay away from Tire Kingdom--just personal bad experience.
Getting tires online is always a possibility, but I've found the cost of shipping eats a pretty big hole in the savings. Then, you are left with the problem of getting them mounted and balanced. That will often take the rest of the savings.
A big part of the expense comes from excise taxes imposed by the Odamna regime. In trying to protect American tire makers, an onerous tax was imposed making anything from Japan, Korea, Germany, France and China vastly more expensive. The American makers like Cooper, Goodyear, BF Goodrich and others saw this as a great opportunity to raise their own prices and did so with little delay.
The only good thing I can say about any of this is that "back in the day" we felt lucky to get 20,000 miles out of a set of new shoes. Today 60,000 is not unreasonable and higher numbers appear with some brand/vehicle combinations.
I've got to come up with a new set of shoes for my JEEP here in the next couple of months, so I will feel your pain. I can get by with slightly smaller tires than you have on the F-150, but we're still looking at $600 before I'm out the door.
Good luck with your search, and keep us posted on the results.
Crusader Rabbit