I made a scalable trading hall.
It's really easy to use, if the trades of a villager don't interest you, just push a button and the villager will let his place for another one.
It can't use zombies to lower the prices, but but with the breeder of impulseSV you can get infinite vegetables, so infinite emeralds.
There is a job site block in every cell, so in one cell the villagers will always have the same job.

I will do a video if it interests you.