MIT is designing an affordable open-source low cost one. This article explains why it’s not as easy as it seems:
“The team is particularly concerned about the potential for well-meaning but inexperienced do-it-yourselfers to try to reproduce such a system without the necessary clinical knowledge or expertise with hardware that can operate for days; around 1 million cycles would be required to support a ventilated patient over a two-week period”
http://news.mit.edu/2020/ventilator-covid-deployment-open-source-low-cost-0326
“any low-cost ventilator system must take great care regarding providing clinicians with the ability to closely control and monitor tidal volume, inspiratory pressure, bpm, and I/E ratio, and be able to provide additional support in the form of PEEP, PIP monitoring, filtration, and adaptation to individual patient parameters.”
It’s not an easy project. But they are hopeful to design one using less than $100 in parts.