A solid weather station should last you at least five to seven years if you pick one with good sensors. You want to buy quality hardware once instead of dealing with cheap, plastic parts that fail after a single winter.
Tech brands usually release updates annually, so wait for Father's Day sales to grab last year’s model. It will have almost all the same features as the newest version, but at a significantly lower price point.
Remember that the 0% period is a deadline, not a gift. If you still have a balance once the 18 months are up, you will start paying interest on whatever remains, which makes the station more expensive than you planned.