Packs can cost from 400-15000 coins or you can buy some with real money. You need to buy 100 packs so the cheapest packs are advisable. However, packs are not the best deal unless you get insane luck and pull a player worth thousands, so it is best to get this trophy after the other Ultimate Team ones so you do not waste your money. You should also sell any unwanted items through trading so you can get more money to buy packs. Packs opened on the web app do not count towards this total. Once you have opened 100 packs (there is no way to track this), the trophy will unlock.