If you haven't already looked into PCs for People, they might be a low-cost option for your school: https://www.pcsforpeople.org/tech-for-nonprofits/#Eligibilit...

PCs for People is a non-profit organization whose mission is to bridge the digital divide (e.g. through sales of low-cost refurbished computers, internet access, and digital skills training).

They refurbish and sell computers to eligible organizations, including schools and offer bulk orders (6+ units) via email at "partner [at] pcsforpeople [dot] org".

If the order is 5 units and below, you use their publicly available online store link at pcsrefurbished.com/sales/salesHome.aspx