How much would you pay for a part of this? The southern 3.5 acres of Simpson's island, long an unofficial campground, will be sold to the highest bidder during an auction July 12 aboard the Island Princess. Ever wanted to escape to your own island? Or in this case, your own half of an island.  The Shingledecker family of Stuart has placed its 3.5 acres of Simpson's Island in the Indian River lagoon just inside the St. Lucie Inlet for sale through an auction aboard the Island Princess next week. Southern portion of Simpson's Island will go to auction     What a buyer could do with the land — inhabited only by wildlife and the occasional camper — is unknown. The land, estimated to be worth $3,700 by the Martin County Property Appraiser's Office, has no zoning or future land use designation.                Auctioneer Tim Hoza, of Karlin Daniel & Associates Inc., said there is some land with higher elevation that could be built on amid the Shingledecker property, but that any plans to build anything from a home to a simple day retreat would be up to the new owner.      "Certainly one person could prevail with having a use approved that another couldn't,  through tenacity and the ability to compromise," Hoza said.         Simpson's Island — which is named after a previous owner — is partially owned by the state. The southern section has been in the Shingledecker family's possession for 40 years. It lies inside the St. Lucie Inlet across from the entrance to the Sailfish Point Marina.     Members of the Shingle-decker family had lived on the southern half of Hutchinson Island before the development on Sailfish Point was built and had used the land for their own camping. They could not be reached for comment Monday.     Martin County Growth Management Director Nicki Van Vonno said she didn't know whether anything could be built and declined to speculate without further research.      The town of Jupiter spent almost two decades in its successful fight against the owners of the 12-acre Fullerton Island, who wanted to put up nine luxury homes. The town rejected permit applications because of the difficulty in providing emergency services to the land, which is across from Burt Reynolds Park in the Intracoastal Waterway. JIM TURNER Licensed Real Estate Broker • FLAB878AU1207  4285 SW Martin Highway, Palm City, FL34990   1.800.329.0036