Two options being considered - Beijing

I am considering staying in Changping instead of downtown to make it quicker access to the Great wall the next morning. However, I am considering that it may be cheaper overall to have a private hire car all day instead of paying once from PEK to Changping and then still hire another car the next day for the wall, Summer Palace and then to the PEK airport. Is it better to just hire a full day private hire? If so, what is the general cost?