Driving around without a dash cam is a gamble these days. Between aggressive drivers and mysterious parking lot dents, having a front and rear setup gives you actual peace of mind. Running this gear usually costs about $350 once you factor in the hardware and a clean professional install.
You can save a chunk of change by buying during spring auto tech sales or major holiday promos when prices dip. Don't try to negotiate the price of an install at the shop like you would a used car; instead, shop around for the best labor rate and let your payment plan handle the cash flow.
The intro window is a deadline, not free money. If you still have a balance left when the 18 months are up, deferred interest or standard rates will kick in on what you owe.