When your car starts bouncing like a boat over every speed bump, you are past due for new struts. Running a car means dealing with heavy maintenance bills, and a full front and rear suspension overhaul usually runs about $1200. The best time to schedule this work is often in the spring or fall when repair shops run slower promo periods to bring in business.
Negotiating the repair price with your mechanic is totally separate from figuring out how to pay for it. You want to lock down the final parts and labor estimate first, and only then look at your payment options. A financing window is handy for spreading out a big chunk of cash, but it does not change the actual bottom-line price of the job.
Remember that the intro window is a strict deadline, not free money. If you still have a balance left on the Citi Simplicity® Credit Card when those 18 months run out, standard interest charges will kick in on the remaining amount.