Something so rare, unique or desirable that it transcends normal concepts of price, often used as hyperbole for something with exceptionally high value (Wikipedia, 2012).
To apply the meaning of priceless, there you go:
Drive to the beach for sun tanning with cheap sunblock applied together with the guy during the day. At night, eating mashed potato looking at the stars creating wondrous memories. The guy is priceless (Tai, Y.Y, 2012)!