Not that many of us will ever have the funds to support a guitar collecting habit or to find the most expensive production guitar in existence and then go and buy it, but it's fun to dream.
It used to be Blackie, a Stratocaster once owned by Eric Clapton but Blackie's fetching price of $959,500 paid by a guitar store in 2004, was recently beaten by another Stratocaster guitar signed by many of the world's most famous guitarists. The Strat was auctioned to benefit a tsunami charity, Reach out to Asia. It was bought by Qatar’s royal family for $1,000,000 US. They donated it back to Reach Out To Asia, bringing in $2,700,000 US at another auction, so the guitar has generated a total of $3,700,000 US.
If you're ever thinking of spending this kind of money on a guitar I'd suggest getting one of the world's most expensive guitar picks to play it with. Made from a meteorite these are a bargain at $110 US for the Astrotone. Available from Meteorite Guitar Picks.