It's very easy to plan a do-it-yourself tour of the Great Wall of China at BaDaLing (八达岭). And it costs only RMB12x2 (total USD4) for the journey there and back.
The Internet is full of postings on how people signed up to tours only to be held at ransom to cough up more money after the bus has moved off. Do not be another victim.
By the way, most of the victims are Chinese nationals from out of town or people who speak some Chinese. The swindlers, or enterprising businessmen depending on how you view them, tend to leave the non-Chinese speakers alone as sign language is harder, I guess.
Follow these steps carefully for a low-cost and enjoyable tour. We just did it last week.
1. Make your way to DeShengMen (德胜门). This is once a city gate of which only the archer's tower is now left standing. The archer's tower is a huge structure that cannot be missed once you are in the vicinity. There are a few bus terminals there. The one you must go to is north of the tower. From the air photo below you can see the buses lined up for the journey to the Great Wall.
2. The nearest subway station is JiShuiTan (积水潭), 500m to the west of the tower. You can also go to http://www.bjbus.com/ to find the buses to DeShengMen from where you are. Each city bus trip costs RMB1, or RMB0.20 if you have a multi-trip card. Taxis can be a cheap option especially if you have three or four persons in your party. Taxis start at RMB10 and covers some good distance before the fare increments.
On my trip, they put in extra buses to the Great Wall. The bus had a sign as in the picture below, which actually means "extra direct bus".
When the staff saw me taking a picture, she helpfully flipped it over to the more meaningful one which says "Direct to BaDaLing" (八达岭).
Anyway, the bus-stop should have this sign. But the crowds there could have moved it from its proper position.
The bus moves off only when filled. The whole journey is on the BaDaLing Expressway, which starts right at DeShengMen. The trip will take about 1.5 hours with the traffic jams on the expressway.
For the return trip, board the same 919 from where you alight at BaDaLing. I guess it is prudent to double check it's the express to DeShengMen.
Have a nice trip!
The entrance fee at the Great Wall in November is RMB40. Credit cards can be used.