A German family (friends of mine) want to send their 16-year old son to Palo Alto this summer for August. They're willing to exchange and take in your son or daughter.
It'll only cost airfare and pocket money.
If you're interested, contact me and I'll put you in touch.
I got my degree at the University of Heidelberg. It's a medieval university town with a castle, lots of paths in the forest, bicycle paths to everything, and lots to do.