A villager's trading prices will fluctuate based on demand, so less-purchased items will naturally go down in price over time. However, prices will also drop if the player has the Hero of the Village effect, which not only makes villagers shower you with gifts but also lowers the prices for trades.

How do you make villager prices go back down?

Lowering trade costs in Minecraft

Do villager prices go back down after hitting them?

Hitting Villagers or a villages Iron Golem creates minor_negative gossip and killing villagers or a villages Iron Golem creates major_negative gossip, raising prices.