I'd just go to Ebay or some store online. After a lot of experience, I just find that buying packs isn't worth it unless you don't need anything except for binder candy.
For me the easiest thing to do to get an ex and star is to buy it individualy and,my first ex is just LUCK i got from a booster pack its a shiftry ex and then my second happened a hour after that i got a JIRACHI EX ahahah see it is just luck,but i felt that both them was quite heavy and the others were lighter ahaha or maybe just my imagination
Buying boxs is much more cost efficent then buying singles. Buying singles of a good ex can cost you a good 25 dollars. If you want 3 different, thats 75. I would rather take 3 random exs+9 holos and 36 reverse holos and good trainers for the 80 then take 3 selected good exs.
I do not know if this works, but try weighing the packs. The ex cards have the foil part around the side, so that might slightly increase the weight of the pack. If all else fails, buy singles on ebay and buy boxes.