I've been playing Pokemon TCG for a few years and a friend of mine just decided to get competetive. So he bought two pre-con dex to learn the basics, and 5 packs to start out. First two packs he opened where EXs, which is great but he's sorta gotten his hopes up for the future. I bought 8 packs at the time and got no EXs at all.
It's seriously all random, but I'd suggest not buying one pack at a time, buy 3 - 4. If you can, buy a tin. They're like 11 bucks and you get 4 packs and a promo EX, plus the fancy tin. The tin and EX alone are great and decent trading material, and you have a chance of getting better cards in the packs. I actually bought a tin while I happened to be near Target for the heck of it, and I pulled an EX (From the pack inside.) (Since I normally don't buy from there or Wal-Mart, what exactly are the opinions behind their packaged packs?)
The best is getting a Box every set or maybe every other set, or at least making it to every prerelease. Boxes are around the $65 - $80 range on eBay, and you can get cheaper EXs off eBay for trading material. If you at least get one box, you should have enough to keep you in circulation for awhile with what you pull to trade others, so that's perfectly fine. I suggest Dragon Frontiers so you can get what you want soon and keep it later for the modifed format.
If you're so worried about EXs in decks, you should know that EXs don't ALWAYS make the perfect deck. Exeggutor is great and is used in an incredibly strong deck that runs no EXs. A different friend of mine uses EXs as trading material for rares and trainers since he's not much of a collector and his decks run great. Kingler d is another example of a currently strong non-EX.
Anyways, hope that helps, and good luck ^^