I do my own estate in Wanatawilluwa. According to my experience coconut plantation is a really good business.
What makes it really good is the capital appreciation of the estate, which is well above the annual profits from the sale of the coconuts.
Further, if you want to have an estate, do it by yourself. I don't advise green field. With green field, the ownership of the land is not an issue. You get the ownership of the land, but every thing else are doubtful.
The variety of the coconut plants by the green field can not be expected to have a long life, like other normal varieties. Normal varieties takes about 5 years approx to start harvesting, but this variety will be sooner. So customers will be attracted, but it will not last long.
This area is in dry zone. So during some part of the year this area gets no rain at all. In order to survive the coconut trees during this season and to maintain the crop & the size of the nuts, it is necessary to have husk pits in the estate. However, since the husk prices are now high many estate owners don't do this. Even the green filed doesn't. If you visit them during the dry season you will be able to see how those trees looks.
At the time of planting also, lot of husk should be placed inside the pit with the plant. But many people who are in the business of selling immature coconut plantations are not doing this. What they do is this. They buy a bare land, clean & prepare then just plant some nurseries. And they water the land for some time & sell quickly.
During dry season the water is very scared to find. So its not possible to water the plants during that time.
And the most difficult part is protecting the immature plants from insects between the age 2 - 6 years. The estates you buy from the green field will have plants which are in this age range. Due to an insect affection a tree can die with in few days. A tree which just starts to harvest at the age of 4 or 5 years would die from an infection if its not identified and treated soon.
So the whole effort would be lost. This is the risk.
Anyway if you can manage these risks smartly, you will really win. Estate values increase from 50% - 100% if you maintain them well.