Owning a classic is a split personality. You get the grin every time you turn the key, and a slow leak of cash the rest of the time. A full paint job sits near the top of that leak. Bodywork, prep, color, clear coat, and the polishing that follows can land around $4,500 for a quality single-stage respray on a driver-quality car, and twice that if you want show-quality work or a rare color. Paint is also one of those things where what you do not see (the sanding, the priming, the rust repair under the old paint) is most of the cost.
The soft window for paint is winter. Shops are slower between roughly November and February, so hourly labor rates and wait times often ease up. That is also when a 0% intro APR card window can do real work: put the deposit and any add-ons on the card at the start of the job, then pay the bill down month by month before the clock runs out. The card is not a discount on the paint. It is just a way to keep your savings intact while the car is in the shop.
The intro window is a deadline, not free money. If a balance is still on the card after 15 months, the regular APR kicks in on the remaining amount and gets charged monthly, which can quickly erase any negotiating savings. The plan only works if the paint is paid off inside the window, so size the deposit to what you can realistically clear in 15 months.