Winter salt eats car paint for breakfast, and keeping a daily driver clean gets expensive fast. Most detail shops get slow in late winter right before the spring rush hits, making that the softest window to negotiate a solid price on a full exterior ceramic coat.
A proper job runs around $1,400 because of the hours required for paint correction before the shell goes on. You want to negotiate the work upfront and use financing strategically so you do not drain your emergency fund in one go.
Keep in mind that 0% interest is not free money; it is just a deadline. If you have any balance remaining when those 18 months run out, the regular interest rate applies to whatever is left, so set up automatic monthly payments of $77.78 right away.