The primary weapon against tanks carried by the A-10 is the Maverick missile. The GAU-8 can do wonders against a tank especially perforating the upper engine deck etc, but it's really designed for destroying soft targets in combination with unguided rocket pods or CBUs. Comparing it's accuracy with PGMs (that it can carry as well) is disingenuous.
Oh, and you seem to be forgetting that the A-10 has had Litening pods for quite a while, giving excellent targeting and ID capabilities.
The A-10 is one of the cheapest a/c the USAF flies, excluding drones which still can't compare with the Hog for effectiveness. There's a lot to be said for the Mark One eyeball in the cockpit. The cost for flying the A-10 would be even lower if the service wasn't continually gutting its support infrastructure.
The Texan/Tucano light prop a/c is always trotted out as the cheap alternative, but the disadvantages are huge. No self-deploy capability, no survivability against MANPADS, single engined so lower ability to overcome mechanical issues, and kleenex for armor against groundfire.