Luckily for many travelers, airfare to China has fallen a bit in the past few years. Increased demand for the tourist dollar has resulted in lower ticket prices for much of the mainland—whereas in the past, cheap flights to China usually landed only in Hong Kong or connected from Taiwan, now you can get a round trip to ticket to any of China's major cities for approximately the same price. This is good news for those that want to avoid Hong Kong and save money. Millions of dollars have been invested by the central government in renovating airports to help compete with Hong Kong's, and it shows.
For the most part, though, cheap flights to China are coming in through one of the main Chinese airports: Beijing, Shanghai and Hong Kong. The international airport in Taipei, Taiwan is also an excellent way to approach the mainland. Tickets to Taiwan fluctuate in price just as often as those to Shanghai or Beijing, so there's a chance that if your have uncertain travel dates, you can find a cheaper fare through this route.
Of course, there are a number of other ways to come by cheap flights to China. As always, the internet often offers the most competitive discount prices, though many prefer to book through a real live travel agent. There are benefits and drawbacks to both of these methods, and it's always advisable to shop around.
No matter which way you obtain your airfare to China, you are going to encounter lower prices during the tourist off season. This will mean having to brave the harsher climates (especially in the north), but it can cut down travel expenses by a large degree. Another trick is to avoid the Chinese New Year, which is when airfare to China escalates dramatically despite, technically, being in the off season.
Inter-country flights have also seen a rise in popularity. Though China has exceptional rail travel options between its larger cities, cheap flights can also cut down on a lot of travel time, especially if you don't have a lot of time to spend and want to see what each region in China has to offer. Now a ticket from Hong Kong to Beijing is often cheap enough that it can be well worth the time to investigate.
Another thing to keep in mind is the existence of a departure tax when you leave the country. Though it has a tendency to change with little warning, it absolutely must be paid, in cash, as you are leaving China. So make sure you find out how much it is when you land so you don't have to struggle through changing your money one last time as you wait to depart.