I know you must have studied the website, and maybe you've already negotiated, but the $130USD / car selection combo you mentioned is for a "Full day Beijing", not GW. It will be a big day trip. I hadn't expected to spend a lot of time at the GW, but it ended up being a great 3-4 hour walk up and down some great stuff with a packed lunch break. Good experience, but we avoided the tourist areas in lieu of the slightly longer drive. It started around 8am and finished close to 7pm.

Btw, I can't imagine anything in Beijing being walking distance with the exception of some of the hotels close to the centre. It's one of those large, flat cities where everything is just spread out. Fwiw, I've been there eight or nine times over the last eight months on business and will be there again in a little over a week.

Edit to add, $130 isn't a huge amount and if it's simple and organised then all the better. Some days are just better to have in place than to have to work at them. One last word though: don't plan to the minute or half hour. Traffic can be a bear.