How is this different than buying an around the world ticket through an airline alliance (e.g. OneWorld, Star)? Those tickets tend to start at around $2000, sometimes less: http://www.oneworld.com/flights/round-the-world-fares/onewor...
Even at low season, if you price out an itinerary starting/ending in North America and hitting all six, using OneWorld's online calculator, it always comes out $3500+. You can get lower if you don't have the six-continent requirement, though.