24 CFR 906.29: Below-Market sales and financing.

A homeownership plan may provide for below-market purchase prices or below-market financing to enable below-market purchases, or a combination of the two. Discounted purchase prices may be determined on a unit-by-unit basis, based on the particular purchaser's ability to pay, or may be determined by any other fair and reasonable method (e.g., uniform prices for a group of comparable dwellings, within a range of affordability by potential purchases). Below-market financing may include any lawful type of public or private financing, including but not limited to purchase-money mortgages, non-cash second mortgages, promissory notes, guarantees of mortgage loans from other lenders, shared equity, or lease-purchase arrangements.