I think the suggestion of looking for a used prince/neos 1000 is a good one.
It's the kind you see in lots of pro shops because it's a workhorse that will last you forever as long as you don't abuse it.
You may want to reconsider the 6pt mounting though. Most of the high end stringing machines that are used at pro events use 6pt mounting, so perhaps you just need to make sure the mounts are the right shape so as not to block holes. I only say this because it would open up your options quite a bit as there are good machines from alpha and gamma anywhere between $700 and $950
Völkl PB10 Mid / Pro's Pro Vendetta 1.20mm @ 50lbs