Alright. I'll second both noles and decurso. You can have any type of life in Beijing you want. All depends on how much you want to get paid. There are many companies, training centers, schools that always look for teachers. You can be on a contract and get paid 10-12,000 with/without benefits. Or it can be less. Also depends on location. I know a lady who worked in a kindy in the south of beijing and her salary was around 15-16,000 a month (of course without benefits). Another friend of mine is a part-timer for New Oriental school. She works only 3 days a week, she has the highest part-time rate (she's been with the school for a long time - the school has different rates according to your experience and students' feedback) and her salary - if there were no cancellations - comes out very high.
I take a bus to my school and it costs me 1rmb one way. I rent my apartment for 2,000rmb in downtown. Apartments' rates in Beijing are so various in the same area due to the fact that next to some international compound you can find a lot of Chinese housing areas so-called "Li" (Nanli, beili, dongli, xili). Those that are government owned and leased to people are cheaper.
The further you get away from downtown, the bigger and cheaper you can find apartments. Like, around the airport area it is possible to rent villas for as much as 4,500-5,000rmb a month (as big as 200+ sqm). In downtown for that big of a place you'd pay 3-4 times more. The only inconvenience is commuting to work, unless you work somewhere around that area.
Food. A lot of really cheap places. Even foreign food stalls with more or less decent prices. If you are a Chinese food fan then you can eat really really cheap. Markets are everywhere - bigger, smaller. Food, clothes etc. Medical services, different activities, events, places to go out to, places to go for a walk... I can go on and on.
What you need to do is make up your mind whether you really do want to move here. Then start looking for a job. And once you are already here - it will be even easier to manage your life etc!