Chairs and umbrella is free at the beach bar next to Orange Fever as long as you eat there, at least they were when we were there in February, the name of the bar escapes me but it's right next to OF on the right, good service too.
$30 at Bikini but very comfortable cushioned chairs. FYI my experience, at least last week, is that reservations for both restaurants and chairs are a necessity ! Could not get chairs at Le String on Thursday…. I understand reservations for the restaurant are a good idea but never thought about chairs!