Building Duplex on Vacant Land

[Lorinda Riley]

I'm new to this forum and to investment properties.  We are interested in a type of hybrid investment property . . . meaning that we want to purchase vacant land to build a duplex for rental property for the next 10-15 years.  Then we'd like to move into the larger unit later in life while still renting out the smaller unit.

We are located in Hawaii and the property we are interested in is oceanfront.  We really like the location (for our own purposes), but at the same time this is an investment, so we don't want to get too caught up in our desires. 

Our concern is that there are very few oceanfront properties in this particular area and we don't want to pass it up.  However, we also feel that the asking price is too high, but since there really aren't any comps I'm not sure how to determine what is reasonable and articulate it to the seller. 

We are working with a relator who has some ideas, but wanted to see if anyone else had some advice on how to make a decision on something like this?  and how to negotiate with a seller who seems to have picked a number out of the air to list his property?