Always strive to learn something useful. --Sophocles

That "not as finely controllable as a 25k$ machine" part is a serious problem for ventilators. Most DIY ventilator models I've seen are automatic ambu-bag squeezers, and the problem with that is that these can't be used more than a few hours because they end up damaging the patient's lungs. There's a Romanian team that's attempting a bag squeezer connected to some sensors that would actually allow enough precision in bagsqueezing to mimic a ventilator's performance, but they haven't cracked the issue yet either. I'm just glad that they're working with a team of doctors and realize what the problem to solve is.