Buying a bulk set

To put it simply, I was at the league for my first time on the day of the platinum pre-release and I noticed I was lacking certain cards that were very effective in any deck. I know a number of these appear in the great encounters boosters and those boosters are pretty hard to come across in decent numbers. What I'm generally asking is should I buy a box display of these boosters to try and get the cards I'm looking for or should I simply buy the boosters whenever I can?

Try eBay first, might work out cheaper to buy the singles