How to Plan Emerald Spending Around Locked Trades
Survey Before You Spend
Before handing over any emeralds, open a villager's menu and read the locked rows. These show what the villager will offer at higher levels, including the emerald cost of each trade. Write down the totals for the trades you actually want.
Budget for Unlocking
Unlocking a locked trade requires the villager to gain experience, which you do by completing its current trades. Factor in the emeralds or items you will spend on those lower-tier trades, because that cost comes before you reach the offer you want. Add it to the price of the locked trade itself to get the true cost.
Buy in the Right Order
Once a locked trade opens, buy from it before spending elsewhere. If a villager has several locked trades you want, work through them in the order they unlock so you do not waste emeralds on trades you will not use.
Avoid Wasted Purchases
Because you can see everything up front, skip villagers whose locked trades do not help you. Save those emeralds for the villager whose full list matches your goals, and you will reach the trades you need with far less grinding.