After a growing through a string of acquisitions and mergers, ride-sharing leader Zipcar (s zip) is now the company being acquired. Car rental giant Avis Budget Group (s car) said it is buying Zipcar for $500 million in cash or $12.25 per share, a 49 percent premium over Zipcar’s share price on Dec. 31.

The deal, which is expected to close in Spring 2013, allows Avis to get into the growing car-sharing market and gives Zipcar a big backer, which can help it grow and make it more efficient. Avis said it can achieve annual cost savings of $50 to $70 million for Zipcar by relying on its expertise in fleet procurement, operations and maintenance as well by increasing fleet utilization between the two companies.

For example, Avis can provide extra cars to Zipcar on the weekends when supply is constrained. Avis said it expects the deal will be accretive by the…