I like that approach. I use it myself in other areas. Used high end electronics from 5 years ago are usually better than equivalent price new stuff of today. It's a myth that prices go down on new tech if you wait. "I paid $2000 for my $50,000 projector plus a $7,000 lens with less than 10 hours on it. 10 years later and I still couldn't buy a new projector for $2000 that is anywhere near as good.
If I could go back to give myself advise at the start of my CNC project on what materials to buy and which approach to take, there is a whole laundry list of ways I could have saved time and money while ending up with a better finished product.
I am kinda intrigued by what I could do with one of those broken CMM machines you see on ebay. They look like awesome machine bases for CNC builds / conversions. They start at $400 and they come with precision granite tables with cast iron or granite gantry beams plus precision rails on the x and y (in some cases). For some of them you would only need to upgrade the Z-axis to something more suitable for the cutting forces. They are certainly more robust than any of those cheap aluminum benchtop CNC machines people buy.
I passed up a whole bunch of good deals on high end / labor saving parts because I was worried that I wouldn't be able to move them from the delivery truck to my work space. If only I would have bought some lifting gear first...