pinhead:
makes no sense either economic nor military, the only 'logic' is PR related, and USAF not liking the A-10 or it's mission.
okey, lets go through these 'replacements'.
drone, lets assume MQ-9 Reaper for the job.
http://en.wikipedia.org/wiki/MQ-9
at 17 million a pop it's actually not that expensive, but it is basically a high altitude bomber and surveillance craft, does not really have the staying power for CAS but it would be damn useful for carrying heavy anti armor weapons as fire support, and overhead cameras for situational awareness.
C130 conversion.
http://en.wikipedia.org/wiki/Lockheed_AC-130
it's a conversion and therefor not that expensive...relatively, high altitude bomber and precision firepower, can actually do CAS.
biggest issue is the USAF chronic shortage of airlift capacity, which this takes away from, secondary issue is to do a good job you need to go low, which makes you vulnerable to manpads.
F-35,
http://en.wikipedia.org/wiki/F-35
anyone saying this craft can do CAS is delusional, sure it can drop some bombs, but dropping some bombs(which are well known for going slightly off target) does not make for good CAS, the gun is also a nono, the official stall speed is unknown, but if it is even as low as double the 220km/h of the A-10 i would be surprised, so strafing runs is a joke.
cost: 153 million USD/unit flyaway.
bottom line, to do CAS you need either a very stable platform very high(gunships) or a durable one slow and low, fast and low(which the F-35 can do) is not such a great idea against non-stationary targets, high chance of blue on blue.
so, replacing A-10(current dollar value around 19 million) with MQ-9 reaper(17 million) and F-35(153 million) and you need both to approximate CAS(but not equal a single A-10), makes economic or military sense....how?
after thinking about it, i think a major problem is you CAN'T micromanage a good CAS craft, it's like trying to micromanage a single soldier, to fluid, and limits the effectiveness too much, this bugs USAF and leaders, delegating initiative is not liked, and very stupid.