As BCBud wrote, local produce is generally reasonable in season, varying on availability and the wholesale cost to the vendor. Unless a trip to Sav is on your agenda, shop in Negril at the level of your needs. If you have a kitchen and cooking a few meals, you will probably be at a grocery story anyway so see what they have there as well as at the small market behind the cashpot in town or veg trucks, carts etc..

You will find a wider variety of fruit at the market than on the veg trucks.

The grocery stores frequently have local lettuce: HiLo, Quality Traders, ValuMaster (smallest produce area). There is a head lettuce with dark green leaves and a looser head than bland head lettuce in the US. Seems like a less-hybridized version of lettuce, including the flavor and texture. I like it.