Reduced building fees for second units, especially those that are affordably priced, were extended by the Board of Supervisors last week to incentivize a key strategy for easing Marin’s acute housing shortage. Under the program, which was continued through next year, homeowners can receive a fee reduction of up to $2,500 for an accessory dwelling unit and $1,500 for a junior accessory unit. That reduction grows to $5,000 if the unit is priced so that…