Owning a car in a cold climate is a chore. Between the scraping and the shivering, winter driving is rough on your body and your engine. Early autumn is the best time to buy a remote starter because shops aren't slammed yet and prices are usually softest before the first freeze.
A good system usually runs around $450. You should negotiate the unit price and the labor separately to get the best deal. Financing the installation with a card lets you keep your cash for maintenance while paying off the upgrade over time.
Remember that the 0% period is a deadline, not free money. If you still have a balance after 18 months, the standard interest rate will apply to whatever is left, making that warm car a lot more expensive.