Avis Budget Group (CAR) is purchasing car-sharing company Zipcar (ZIP) for $12.25 per share in cash, or $491.2 million, as it looks to expand its reach to city dwellers. Avis shares rose nearly 5% to just under 21. Zip share jumped 48% to 12.23. "We see car sharing as highly complementary to traditional car rental, with rapid growth potential and representing a scalable opportunity for us as a combined company," said Avis CEO Ronald Nelson.