Is $700 reasonable for four mounted, balanced and road warranty?
If they are the LT versions (load range C) that is a good price. If they are the P/SUV tires (standard load range) that is a pretty typical price.
I have run LT265/75-16 AT3s (load range C) for 2 1/2 years, 46K miles on my 3rd gen. I have been very happy with them. They still have almost 1/4" of tread left (another 10K miles probably) but I'm anxious for some new ones. I have run over 500 miles of midwest Forest Service roads with them - lots of sharp limestone, ledge rock, and thorns. I've never had a flat (but people with me have), but they are pretty chipped up from the abuse. They are great in the snow, and on wet roads they are unbelievable. I ran down the highway about a month ago in a very heavy rain at 70 MPH with no hydroplaning at all.
As noted in the link above, Overland Journal chose them as the Editor's Choice and the Value Award in their AT tire test (other tires were BFG AT KO, Dick Cepek Fun Country, Falken Wild Peak A/T, General Grabber AT2, Goodyear Wranger All-Terrain Adventure, and Toyo Open Country II). They said 'The Cooper Discoverer AT3 was the overwhelming winner and a genuine value'. Also, 'The AT3 demonstrated superior ride quality, NVH, and skid pad handling; it cannot be overstated how well these tires perform overall on pavement'. It had the fastest times on the 90 deg wet turn (55 MPH - BFG AT did it at 32 MPH), the dirt oval (75 MPH! - 15% faster than the 2nd rated tire), and was one of three to successfully climb a 38 deg granite slab. Testing was done by a professional test driver who tests tires for Toyota (Tacoma and FJ), so it was a real, scientific test, with instruments (not a 'we liked this one best because' test). The article is definitely worth the price of the magazine ($12 at Barnes and Noble, Summer 2014).
I run mine at 40 PSI. That's where they get the best mileage. I gave $700 out the door (mounted, balanced, tax) at Orscheln farm supply. They have a buy 3, get one free sale about 4 times a year. The next one starts Sept 16 and I plan to replace mine then.