Newbie to Pokemon TCG

Well i recently started looking and buying into pokemon cards, i have always been a fan of pokemon.
now i understand the rarity and different types of cards and stuff, but what i didnt know was where do poeple generally get their packs from

i have bought some things from eb games so far, and i realise that, the big retailers (big w kmart and target) have the lowest prices, which is why they run out of stock the fastest, and eb games and stores like that charge a bit of premium because of their availability

i dont really look for the most expensive cards, to sell or buy or stuff, i look for things with promos, and guaranteed cards, that i really want to add to my collection,

would be great if i got some advise on how to do this in a cost effective way, (and also how are the local card shops, and would they be more expensive then retailers?)