Projector headlights change the whole look of your car and actually let you see the road at night. Upgrading the assembly usually runs about $550, and you also have to factor in installation time or shop labor if you are not doing it in your driveway. Summer is the best time to look for clearance deals on lighting tech as retailers clear shelf space.
When you are buying car parts, you always want to separate the price negotiation from how you pay. Get the best price on the hardware first, then figure out your payment strategy for the total.
Remember that a 0% intro APR for 15 months on purchases and balance transfers is a deadline, not free money. If you still have a balance left when those 15 months are up, the standard interest rate kicks in on whatever is left over.