A good tint job saves your upholstery from fading and keeps the cabin bearable in the summer heat. Prices typically hover around $300, but you should wait until spring when shops drop their prices to attract seasonal customers.
You want to negotiate the labor cost before you even mention a payment method. Once you have the final number, you can use a credit card to break the expense into manageable chunks.
That 0% offer is a window of time, not free money. If you have any balance left after those 18 months, the bank will start charging you interest on the remaining amount.