The National Park Service is offering free admission to over 100 parks during certain weekends this summer.
Colonial National Historical Park which includes Yorktown Battlefield is one of those parks that will waive the entrance fees and some other fees July 18 and 19 and August 15 and 16.
Colonial also includes Historic Jamestowne (the original site of the Jamestown settlement), the Colonial Parkway (no admission ever for that of course), and Cape Henry Memorial, the location of the first landing of the Virginia colonists in 1607 on the oceanfront at Virginia Beach.
The fees usually average $10 per person, so this is quite a savings for those weekends.
You might check your own national park (www.NPS.gov) to see if it offers free admmission also.