OM, do you have a Golden Age Pass? That will get you into all National Parks like Yosemite and is pretty cheap.

From the NPS website-
http://www.nps.gov/fees_passes.htm

America the Beautiful – National Parks and Federal Recreational Lands Pass – Senior Pass. - Cost $10.


America the Beautiful – National Parks and Federal Recreational Lands Pass – Senior Pass
This is a lifetime pass for U.S. citizens or permanent residents age 62 or over. The pass provides access to, and use of, Federal recreation sites that charge an Entrance or Standard Amenity. The pass admits the pass holder and passengers in a non-commercial vehicle at per vehicle fee areas and pass holder + 3 adults, not to exceed 4 adults, at per person fee areas (children under 16 are admitted free). The pass can only be obtained in person at the park. The Senior Pass provides a 50 percent discount on some Expanded Amenity Fees charged for facilities and services such as camping, swimming, boat launch, and specialized interpretive services. In some cases where Expanded Amenity Fees are charged, only the pass holder will be given the 50 percent price reduction. The pass is non-transferable and generally does NOT cover or reduce special recreation permit fees or fees charged by concessionaires.