The two beach areas at CSS are private and vendors are not allowed to just "walk on" to the beach to sell to guests. There are certain vendors set up near the main pool that sell handmade items but they do not do hair braiding. You can get you hair braided by the people in the salon at CSS. One of the couples we go with has her hair braided in the salon every year. I'm not sure of the costs though. Jed, if your listening, can you provide some insight into this?
The vendors on the beach at CSS are very limited, 1-3 per day, typically with carvings, art, woven bags and hand-painted stones, etc. The girls from the salon come over to hair braiding, so you don't have the many options as you would on a public beach like in Negril. Unfortunately I do not recall what the pricing was, but hopefully someone else can speak to that.