Set prices to include settlement costs, optional upgrades, etc., to the extent possible. Then these items can be included in the mortgage and down payments can be lower. Develop a strategy for appraisals, depending on your needs. Recruit effectively to ensure that all units will be occupied as soon as they are completed. Take full advantage of the clustered housing model.
Common walls save in construction - and in energy use.
More efficient utility lines. Build according to current budget constraints, but design in possibilities for future additions to private houses, common house. Minimize the menu of optional upgrades. Even if this doesn't affect the cost to low-income buyers, it will minimize palpable inequalities after you move in. Be willing to use less expensive materials.