A good power station should keep your lights on and your phone charged for a long weekend. If you buy a cheap one, you will end up replacing it in two years. Aim for a high-capacity model with LiFePO4 batteries because they last for thousands of cycles and will not die after a few seasons in the garage.
New models usually drop in the spring, which means retailers slash prices on last year's inventory. You do not need the newest bells and whistles for a campsite. Getting the older version during a spring sale can save you a few hundred bucks while still giving you plenty of ports and reliable power.
This is not free money, it is just a way to delay the cost. If you still have a balance after those 18 months, the interest rate will jump significantly and make that power station much more expensive than the original price tag.