Trading miles for mortgage dollars But with the cost of gas hovering around $3 per gallon on average in the U.S., it's worth considering whether a shorter commute would pay for the incremental cost of a more expensive in-city home. Assuming a full-time job, $3 gas, 26 mpg and 50 cents a mile for maintenance and no parking fees, a 50-mile roundtrip commute costs $646.15 a month, or $7, 753.80 a year, according to the City of Bellevue, Wash.'s, Commute Cost Calculator. Moving closer to work boosts your house-buying power. Everything else being equal, a 10-mile, roundtrip commute costs just $1, 550.76 yearly -- saving about $6,200 per year, or $517 monthly. That can add about $80,000 to the total amount of a mortgage loan, says one Chicago lender. The rule of thumb: Each $250 a month you can free up for mortgage payments equals roughly $40,000 more you can borrow at current rates (using the recent national average of 6.5%), says David Kasprisin, district sales manager for National City Mortgage Co. in Chicago.