I think one of the first things to consider is if you're buying a new one or a used airboat.
New offers customization and warranty, but comes with a higher price.
Used can be a great value, but requires more careful inspection.
Payment options involve marine lenders, banks, credit unions and with some manufacturers offering in-house financing but your options also depend if you're getting a new or used one.
Regular maintenance is key, but again, the extent of servicing varies significantly between new and used boats.
Then as for storage, the best practice is keeping your airboat in a dry place, out of direct sun, and use a quality cover.
After use, especially in saltwater, clean it thoroughly to prevent corrosion!!