A $4,000 annual maintenance and repair budget is $333 per month. If you bought a $300,000 home with 20% down and a 30-year fixed-rate loan at 4.75%, your $240,000 mortgage would cost $1,252 a month, according to the Mortgage Loan Calculator.A $333 monthly maintenance and repair budget would equal nearly 27% of your principal and interest payment.f you bought a $300,000 home with 20% down and a 30-year fixed-rate loan at 4.75%, your $240,000 mortgage would cost $1,252 a month, according to the Mortgage Loan Calculator. A $333 monthly maintenance and repair budget would equal nearly 27% of your principal and interest payment.