You asked for advice, so my advice is the following:
1) First, try to debug the issues with the computers you have now. At first, don't worry about distros being 100% fully FLOSS distro. No distro can truly be that way, even if they report that they are, they are just closer than the rest. As long as you can see the source code, you have no reason to worry. What kind of things are you worried about, which particular programs or libraries ?
Anyway, try several distros, even Window$, and see if there are hardware issues with the machines or whether there are software issues (usually misconfiguration).
No laptop is too old to be useful, just try a lighter distro.
2) Second, don't you think you'd save money if you went out and bought yourself a real, new, computer instead of wasting your money on junk from ebay that will never add up in value to a new computer ? There are cheap, new computers out there, many even that come with Linux installed or choice of no operating system, and one that come with a warranty and that come intact without missing parts or broken pieces.
This is just my advice, take it or leave it. May the force be with you