Getting into a frozen car in January is miserable, but paying peak winter prices for a remote starter makes it worse. A quality unit plus professional labor usually runs about $500. Late summer is the smartest time to buy because audio shops are quiet and open to deal before the first cold snap hits.
You want to handle the hardware selection and lock in a shop rate before installers get backed up for weeks. Once you settle on a price, you can use a tool like the Citi Simplicity® Credit Card to break up the invoice without owing interest fees.
An intro window is a strict payoff deadline, not free money. If you still have a balance when the 18 months end, interest kicks in on whatever is left, so clear the full balance before the window closes.