you could checkout the website taxistmaarten.com, but it's been forever since they've published the rates by zone. They keep showing "New rates coming soon", but they've been showing that for about two years now. Carol's estimate above is probably correct at $40 USD. And, although you don't have to, I always tip the driver five bucks (because the majority of them are great and they've given me a lot of local advice over the years). Unless you are landing at PJIA at a real 'off' time, there should be a whole host of taxis to choose from. And, BTW bring cash for the taxis.