Graybeard
I am utterly stunned, but at least you are showing your true colours. And studiously ignoring many of the counter arguments to your, IMHO, naive viewpoint.
They cannot justify the cost of new planes for the job, so the USAF can't either.
The A-330 may do fine as a tanker, once converted, but it is far too expensive for the job. So is a new 767. We taxpayers deserve fiscal responsibility.
Your argument is typically short-termist. You don't work for the British Government do you?
If you buy and convert second hand airliners, even if there were suitable numbers available - which there aren't - you would have to pay to convert, pay to modify to the same standard, pay to fit with DAS and secure comms etc and then pay to maintain an ageing fleet. You would then have to replace that fleet in 10 or 15 years, maybe 20 at a push. If you buy second hand again you have to pay to maintain an ageing fleet which you might get 10 or 20 years out of before you have to replace again.
Now which one of these will end up more expensive than buying a new fleet, which has a better capability than anything else on offer at present, in terms of whole life costs? That's fiscal responsibility for you.
You are not going to find sufficient standard mod second-hand types to meet this requirement. If they aren't to the same mod state then your maintenence costs go up (RAF Tristar and VC10 experience, and USAF KC135 experience), or you have to pay to mod them to the same standard as opposed to getting them all to the same standard straight off the production line.
Additional KC10s once the 60 order was complete? Who knows? Maybe the USAF had enough tankers by then and didn't need any more. Or they decided they had higher priorities than more tankers. 757 as a tanker? Forget it! Looked at by Boeing (and others) and ditched as impractical!!
By your simplistic argument none of the major airlines should buy new aircraft either. If the USAF can't afford new then why should the airlines. And why don't the USAF deserve the best that there is? As I said before, and a point you ignored, the KC135 fleet has lasted as long as it has because they were bought new and not converted from some knackered airline stock. That is fiscal responsibility and I would suggest excellent VFM for the tax payer.