If you're only replacing all 6 because of age and not because of damage or excess checking, why not just replace 4 in the rear this year, and 2 in front next year? Or the other way around?
With that quote, you're looking at $678 per tire, that's way excessive in my book. I just found those Toyo tires for $485 with a quick search. M&B should be $40 each, replace the stems should be another $7 or so. Total of $532 each tire typically, M&B.
You'd likely save $876 just by shopping around. Or waiting until you're in a different area because sometimes all the shops owners in one area hang out with each other.
I always buy truck tires for the better deals, and IMO, longer life, so I buy from Amazon, get free shipping with a Prime membership (takes 5 days because of the weight), and have them installed at Love's tire stores for the $40/each M&B. The Double Coin 295/75R/22.5 tires are $286 each right now. So the six of them, M&B, would come to $1998. Saving over $2,000 from the quote you got.