Compared to taxis in Western countries, taxis in China are relatively cheap. Again, make sure you write down your destination in Chinese since your chances of finding an English-speaking driver is slightly better than finding a Chinese-speaking driver in New York City (on a side note, Beijing has 5 times more taxis than NYC).
Though it varies from city to city, taxi rates are usually fixed for the first 3-5 kilometers, then somewhere around Y2-3 for each additional kilometer. Make sure they turn on their meter, otherwise get out immediately (See “Scams“). No need to tip either.
Another option is to hire a taxi for a half- or full-day. You’ll need to negotiate exactly how much you’re paying for a flat rate (for all passengers, not per-passenger!) and spell out where you want to go. As a very general guide, you might expect to pay about Y300-500 to hire a taxi for the day (as well as paying for your driver’s lunch).