An Extra 300L and an amateur-built RV-3 collided in flight while flaring to land at St. Augustine Airport. The Extra suffered minor damage and the RV-3 was substantially damaged. No one was injured. The Extra pilot said he was on a sales demonstration flight with a prospective buyer and announced the flight inbound on the airports Unicom/CTAF, apparently without success. They heard other airplanes announcing their positions in the traffic pattern for runway 2 and made a standard entry into a left downwind at 800 feet behind a Cessna. As he flared to land, he felt a bump similar to a hard landing, then landed straight ahead and saw the RV-3 on the runway behind him. The RV-3 pilot said he overflew the airport at 1,500 feet and entered a left downwind for runway 2, reporting his position on Unicom/CTAF. While on final approach he saw a Falcon jet back-taxing on runway 2 after landing on runway 31, so he went around and took up a position behind the Cessna. He reported his position on short final. As he was touching down, he felt an impact coming from above and saw the Extra land.