You can earn 5,000 United miles for every $10,000 financed on a home equity loan until November 15th. The offer then reverts to the usual 1,300 miles per $10,000.
Since some of the offers which may be available under this program have the bank paying relevant costs such as appraisal fees, the only expense is interest — which you’ll pay for just as long as it takes you to withdraw the funds and pay them back. Then once you discount for the tax deductibility of the interest you do pay, and the fact that you’ll likely earn some interest while the funds are temporarily parked before being paid back, the cost should be next to nothing for a large chunk of miles.
By the way, the 250,000 miles assumes an equity loan of $500,000. Admittedly most of us don’t have that much equity in our homes.