It will all depend on how much you use the spa and what you use to sanitize. Filters will vary by manufacturers but a normal pleated filter should last about 18 months of continuous use. Some spas have multiple filters and some have "special" filters which if used will determine the cost of filters.
As far as chems, a daily soaker sanitizing with chlorine or bromine can probably maintain the spa with about $70 - $100 per year. All you really need is either chlorine or bromine, non chlorine shock, filter cleaner and metal sequesterer, stain and scale and clarifier to use if and when needed. You will also need a test kit or test strips to analyze your water and some pH up or baking soda, ph down and possibly calcium increaser. If you add silver cartridges, enzymes, "specialty" products, etc the cost can easily double or more.
Every five years or so you will have to replace your cover, cover lifter and headrests if you have them (maybe sooner if you use ozone). Replacement covers cost about $400, lifters about $200 and headrests about $200 depending on manufacturer and quality.
Great, thanks!!! I'm learning a lot here. I'll have to look into the Grandee and Vista as to the type of system it uses to calculate the cost of the filters, ect.