That depends on your interest rate, your property taxes, insurance premium, and type of loan. You can do a Google search for "mortgage calculator" and just plug in the figures. To that, add 1/12 of the yearly taxes and insurance. The average insurance policy is probably in the $500 to $600 range. On a house selling for less than $20K, you will probably be paying less than rent; however, don't forget to factor in the monthly cost of maintenance, too, if this is a fixer-upper.