Milepost 5 units costing below a certain amount ($150,000 I believe, but not sure) are subject to resale covenants enforced by a third party nonprofit that allow you to earn no more than two times the annual CPI growth OR fair market value, whichever is LESS.

They also require owner occupation.

This is similar to what the Portland Community Land Trust does to maintain permanent affordability.

I'd contact Milepost 5 with further questions about it, because I lack further detail.

Hope that helps.