Whenever you trade with villagers, they raise their prices. This occurs even if their prices are affected by curing them or another villager in their area. You have to wait a couple of cycles of them working at their workstation for the prices to go back to being normal.

Steps to reproduce:
1. Cure a zombie villager.
2. Trade with the villager.
3. The price will go up, more and more the more times you trade with him without waiting a couple of in-game days.