Consider a much cheaper alternative which might in fact be a better rifle:
The rifle above is Kalashnikov's ultimate sporting rifle, the Vepr II, and can be had for around $500, last I checked. It features a medium heavy, chrome-lined barrel mated to an RPK (squad light machine gun) receiver; yeah it's stamped, but it's the strongest stamped receiver ever made. The thing is very accurate and, in all likelihood, much more reliable than an AR-10.
Veprs come in 223 nd 308, of which the 308 is the obvious choice for somebody who could only have one gun. 308 is your most generally useful rifle calibre. It can basically kill anything which walks, is inherently accurate, and surplus ammo is dirt cheap and will likely stay that way since NATO machineguns still use 308.
Veprs use the usual Eastern-block type slide mount for scopes.