We recently did a visa run. As with many people who live in China, we have to leave the country every 60 or 90 days to reactivate our 1-year visas. We recently decided to try the Beijing-Erlian visa run rather than the traditional Beijing to Hong Kong run. Here are a few details on how to make your visa run a quick success:
1) There are loads of buses that go to Erlian, you can leave from any one of the stations, and it is easy to call ahead of time if you speak even a little Chinese to ensure the buses leave on your scheduled day. Here are the Beijing Long Distance Bus Options.Or, a few other options on how to get to Mongolia.
2) 
Once you arrive (and if you take the bus you’ll arrive at 3 or 4:00am) you may need to stay at a hotel for a few hours until the border opens. It opens at 8:00am. If you arrive at the bus station you can easily find a driver to take you to a local hotel. Bargain, but you should be able to get the ride and the hotel for under $12 USD. Prices should be in Chinese. The hotels are not great, ours was heated by a stove and had wooden beds and a squat hallway toilet, but we only stayed a few hours and it was much-needed rest after 11 hours on a sleeper bus.
3) 
Crossing the border takes patience. You have to get a cab to the gate. Make sure they use the meter, as they’ll try to charge triple what the meter would have. The cab drops you off at the border, then you have to negotiate with a jeep driver to take you across the no-man’s-land to the actual Chinese immigration building. No walking allowed!
4) You use the same jeep to get all the way to the Mongolian immigration side and then through that to the first town across the Mongolian border. Your jeep should cost about 50RMB or less. We negotiated hard and paid only 30RMB, but we also went all out and even included one of the Chinese border guards, who was extremely helpful.
5)
If you want, you can easily get your jeep driver to drop you off at the city square, otherwise you can simply turn around without leaving the Mongolian border zone and negotiate with a new jeep driver to take you back to the Chinese side. Getting back to the Chinese side is cheaper and easier as most Jeep drivers have limited loads.
6) Once back in Erlian, you can take a cab from the bus station in Erliain to Beijing for around 200RMB a person. The bus is 200RMB as well, so if you want to save some time, the cab ride is 7 hours while the bus ride is a grueling 11. I prefer the bus as its a sleeper unit so you can relax, sleep and even read.
7) Your visa will need to be registered once you get back to China. Good luck!
This seems very economic way for visa run, although the condition of accommodation Erlian is not desirable but one day stay you can bear it.