I've never been to Freeport, but I did go to Nassau; and I reckon it's a similar port. Once you disembark and get into the tourist area, there will be tons of people coming to you and asking you if you want your hair to be braided (as well as tour guides coming to you and asking if you want a tour). Just be sure to stay in the tourist area for safety reasons.
When I went there, it was $2 per braid; and I thought it was a tad too expensive so I refused. I met this girl on my cruise who got her whole head braided; and she told me that it was around $70!