Duels of the Planeswalkers 2015 actually costs money, but on the other hand Origins is F2P with a limited card pool and weird deckbuilding restrictions (up to 4x commons, 3x uncommons, 2x rares, 1x mythics). But the again it's free.
Deckbuilding often comes down to what you enjoy about the game. Most people would prioritize winning and therefore spend money on some top-tier deck that gives them the highest chances for winning whatever, while I tend to enjoy building my own quirky decks over winning tourneys, so I'm okay with slowly trading my way to whatever off-beat deck I want to run.
Standard currently has feches in it, so you might consider picking them up while they're still "cheap" since they're used in all eternal formats. On the other hand, the Zendikar duals aren't nowhere near as powerful or as desireable as the fetches, so they're probably going to be cheaper to obtain in the colors you intend to play with a lower budget (however, they won't be nearly as useful as fetches post-rotation).