Don't even think about taking out a reverse mortgage for a measly little $700 property tax bill. You knew that was coming, so why didn't you save up from your income? Poor planning.
Reverse mortgages are only for retirees over 65 who own their home free & clear. It is a mortgage, and your home will be foreclosed & sold by the lender when you die, or is due on sale if you sell before then. This is a rather expensive type of mortgage, they send you monthly payments until you die, but there are fees and points to pay, and often interest is higher than on a regular mortgage. Your heirs probably will not get the house! Also, that home is not worth much, so monthly payments will be very low, if any lender will go to the trouble of writing a reverse mortgage on it to begin with. Even if you are retired, over 65, and need to increase your monthly income, you won't get enough fast enough to pay that property tax.