Late May in Iceland gives you nearly endless daylight, thundering waterfalls fueled by spring melt, and clear roads before the summer tour buses arrive. It feels like driving across the moon. If you wait until July, the prices for rental cars and roadside cabins practically double.
A solid week driving the Ring Road runs about $4200 for two people doing it right. You do not have to part with that cash all at once if you give yourself a buffer before you book.
Remember that zero interest is a deadline, not free money. You still owe the $4200. Set an automatic monthly transfer for that $233.33 immediately, because if you leave a balance past that 18-month window, standard interest kicks in on what is left.