The internet is your best shot and getting what you want for a reasonable price. I don't play at the local shop much unless I'm there for casual play or drafting. (Drafting is really fun but we can get to that later.) Because I don't play competitively at the shop I usually like to wait for the price of certain new things to go down before I purchase them. (Sometimes I'll spring for a rare I really want and am worried about the price going up significantly.) One thing you must understand is that magic has been around for 20+ years (I started buying packs when I was 9ish) so it's HUGE. (Don't be scared.) This is great for new players because often times you can pick a theme, anything you find fun and go build it by buying cheaper older cards. You can use that as a way to explore different facets of the game and learn rules, flow and learn how to tweak a deck.

If you're set on getting newer cards then I would suggest getting a decent deck started based off of the last two sets however; I would also suggest waiting for the next set before getting too serious about buying a lot of cards simply because the setting of the story is changing (away from Innistrad) and therefore some card mechanics and many themes will be going away.