The statistics for YTD 2013 are 13.67% for MLS zone 30 which includes Shelter Island, Southold and Riverhead Townships. This is based upon 33 recorded transactions on MLS. This is a statistic, but should not be applied to any particular sale or purchase that you contemplate. These discounts are from the last listed asking price, not the starting price on a particular listing, and does not take into consideration that the property may have been previously listed with another broker, or with the same broker at a different price.
Some properties sell at or close to their listing prices, a few may generate a premium from the ask, and still others sell at a severe discount, depending on how ambitious their price starting point was.
Please check with a local broker, as the purchase of land could be a tricky thing, especially if there are not permits in place for your ultimate use.