[turtlebits]

You can get a commercial unit for under $400 USD. Search for "Pioneer 50 ERV", which claims 97% efficiency or look on aliexpress for units under $200.

That said, I find these "regenerative" heat exchangers too limiting as they generally only work for a single room/space.

[open_erv2]

My price is for a pair, remember, not one. And those pioneer things don't work very well, poor flow and efficiency unfortunately. They claim high efficiency but it's only at the lowest flow rates and not the average for the cycle, only at the beginning of the cycle. There is one company that keeps emailing me trying to sell me units wholesale, I keep telling them to send me actual test data and then I might buy some (for testing), and they never do.