Jah'Bs has cabins that are $30 per night and you might even be able to talk them down a bit lower. They are very basic and across the road from the beach. We stayed there about 10 years ago. Mostly locals but it was kind of a neat property with porches that were nice to sit on an have coffee. Ours had a kitchen and a our own bathroom.

http://negril.com/jahbs/rooms.html