When zombifying a villager, if their prices are already at their minimum, the prices will increase after being cured.

To reproduce

1- Find a villager with trades

2- Zombify and cure it until its trades are at their minimum (1 emerald per trade)

3- Zombify and cure it once again

The trade prices should have gone up and no longer be their minimum.

I just experienced this with a novice librarian. After 4 cures, its paper and enchanted book trades were all at their minimum. I cured it once again just in case a locked trade was not at its minimum only to find that its trades had jumped to 18 papers per emerald and 24 emeralds per book. Between zombifications, I did not do anything that would normally raise trade prices, such as harming villagers. This really hurts profits and isn't the first time I experience this. I have not yet tried zombifying and curing it once again. 

I am playing vanilla on a singleplayer survival world without datapacks that should alter villager behavior.