This sounds like a great initiative. I follow an education technology person on Twitter: https://twitter.com/philshapiro they talk a lot about procuring laptops from eBay and then installing distributions such as Linux Mint on them to refresh them and loan them in their library. It might not be something every org has an appetite for but it's one option.
I can also speak to the quality of System 76 laptops that Chuck mentioned. The high-spec ones are great for development, but there may be combinations of machine that are much cheaper and might offer a good solution for your purposes as well.
All the best,