The mark-up is not what you think at all.
I put myself through college working at a tire and auto shop in North Carolina. On every tire we sold besides 19.5s and 22.5s our mark up was 30 bucks a tire. This included mounting and balancing and free rotations for the life of the tire. Tires are pretty much one of the most important things to spend money on, on a vehicle, beside steering components and brakes. Spending the right kind of money on tires is a wise choice if you drive anyone else around in your truck. 30 bucks a tire is not a huge mark up, now I am sure there are others that mark up less and others that mark up more, but when you look at everything 120 bucks mark up for 4 tires is pretty reasonable. There is roughly an hour of labor, lead weights, tire slim to mount the tires, old tire dissposal fee, free brake checks, and typically underhood fluid checks. Plus the shop has to pay its bills and pay its employee's. Our mark up was exactly the same for every single tire we sold. It didnt matter if it was a BFG M/T or a 30 dollar no name piece that no one has herd of.
I would complain about spending money on something else, like water rather than tires. Now a stupid bottle of water is anywhere from a buck to a dollar fifty. Thats ridiculous, but it sure does taste good.
Do not take this as a bashing on you post and getting upset, its more of an informative post letting you know what the mark up is and how your money is spent.