I might be wrong on the free chairs at both beach bars, but pretty sure that either Le String or Orange Fever was free. 5$ is a pretty good deal nonetheless. Forgot to mention, we also went to 321 on Friars Bay on this trip, nice place and great staff with free chairs since we had lunch and drinks.
Just to add some additional context, last year we went to a birthday party for a friend on the beach at Kon Tiki with about 25 people. It brought in a lot of $$ for Kon Tiki but they charged everyone 25$ for chairs and umbrella.