I prefer the AR-10 to the AR-15, but then I'm just a 30 caliber guy. In fact, I don't own much that isn't 30 caliber or bigger. The local gun shop guys call me a recoil junkie. The AR-10 has pretty low recoil, and the round itself is far more inherently accurate, and far more effective. The point being, if you are going to pony up a big price, get all you can get for your money. Depending on how things go, the AR-10 308 may not be that much more expensive to shoot than the AR 15 223/5.56 NATO.
Yes, the AK and SKS stuff in 7.62x39 is cheap to shoot. It is also less accurate and less powerful, so it has less utility than the 308 in the AR 10, unless you just want to spray a lot of cheap ammo from a cheaper rifle.
With guns, you do not always get what you pay for, but you rarely if ever get what you do not pay for. Meaning if you pay a lot less for a rifle, expect a lot less rifle.