These are only my personal thoughts and views:
Generally the prices range from 4,000.00 -15,000.00.
Anything above this is likely trying to be rented out by another expat or a local who is trying to get an expat for a lot of money.
There are two main areas (or sides) of Lamma, Yueng Shuen Wan is busy with restruants, bars, and mini-stores. It also has an HSBC bank and a post office along with a large population of expats, families and loads of children and loose dogs. Rent is higher in this side due to population and convienence.
Sok Kwu Wan side is a more local area with one row of about 12 different seafood restruants, one or two min-stores, and more locals than expats. Rent is lower here due to longer time between ferry's to Central and less convienence as far as shopping goes.
If you are interested, I have a 3 bedroom available on the Sok Kwu Wan side of Lamma for 6,000.00 per month (swimming pool, close to beach, 750 sq ft, large yard/garden, maid, green view, sea view, rooftop).
Will send details per request. Good luck with your search and hope my thoughts and views have helped.