A good tint job keeps the heat out and stops your dashboard from fading, but it is a luxury that adds up. The best time to book is early spring before the summer heat rush sends shop prices climbing.
You are looking at about $400 for a quality service on a standard sedan. Since this is a one-time upgrade rather than a recurring cost, you can manage the cash flow without hitting your savings account hard.
That 0% window is a deadline, not free money. If you have any balance left after the 18 months are up, the bank will start charging you interest on the remaining amount.