Savannah and Charleston are built for slow walking, Spanish moss, and very good food. Late autumn or early spring gives you the best weather, right when the Lowcountry humidity drops and you can wander the historic squares all afternoon without melting.
A realistic long weekend covering both cities runs around $1,600 for hotels, gas, meals, and tours. If you do not want to pull that straight out of savings, you can spread the cost over time without paying extra in interest.
Remember that a zero-percent promotional window is a strict deadline, not free money. If you do not clear the full $1,600 balance before the 18 months end, regular variable interest applies to whatever amount remains.