Determine the opportunity costs, of using required funds for closing (i.e., down payment plus all closing costs), rather than investing the funds and earning an effective rate of 6.5% yearly. The down payment amount will be 20% of the purchase price of the house you selected. For estimation purposes, closing costs will be $3,000.00. 1. Calculate the amount of forgone interest on investment 2. Add the sunk closing cost amount for the following periods: a. Two years b. Three years c. Six years d. Eight years House for Buying: 3 bed 2 bath. 1628 sq foot. Buying price 235,550. (5110) is 20% of closing cost.