Using a piton may seem simple—just hammer it in—but in reality, a safe piton protection point demands very high standards. In China, there have been cases where climbers using pitons fell and the protection failed, due to issues with the rope, the piton, or other factors. The injured climber had to rest for several months.
Pitons designed specifically for mountaineering usually come with labels prohibiting their use for rock climbing.
The general price of pitons in China is around several dozen yuan. Knifeblades are relatively cheaper, while angles, lost arrows, and universals are slightly more expensive.
One more suggestion about pitons: if placed well, they can make good protection points, but often mean they can never be removed. Pitons can also cause permanent damage to the rock. If you aim to develop crack climbing skills, it’s better to use cams for protection. In fact, using pitons is often more expensive than using cams, and you also have to carry a heavy hammer during climbs.