Carrying four bikes on your vehicle is serious business. Between the rack itself, installing a hitch receiver, and taking a small hit on gas mileage from the extra weight, setting up a proper rig costs real money. Prices are softest in late fall, right when shops dump summer gear to make room for snow equipment.
You want to negotiate the rack price on its own before thinking about how to pay for it. Once you lock in a clearance deal, using a zero-interest card window helps you break up the cost without touching your emergency fund.
Remember that a 0% intro period is a strict deadline, not free money. If you still have a balance after 18 months, regular interest rates apply to whatever you owe.