There is a very simple way to start building decent decks in very little time. It happens in three steps:
1) Realize that grinding FGs and grinding AI3 are essentially the same -- you're grinding. If your goal is to have fun by doing something other than grinding, you need to look into PVP, not toward FG farming.
2) So, get good at PVP. Really good.
3) Win tournaments. Every tournament win nets you 5000 electrum and a rare card you can sell if you want.
Alternately, you can donate $5 to get just over 1000 ep.
Alternately, you can cheat, but then you'll get caught and have to stop playing anyway.
So, either spend money (not a great option), win tournaments (not an easy option), or commit to grinding for electrum as efficiently as possible. In almost all cases, that means using a Life rush w/Heals to get fast EM victories over AI3 until you can upgrade 6 cards, then a Golem rush to speed-grind t50 to earn 3xLobotomizer, then RoL/Hope to speed-grind FGs until you can build Shakar's Revenge and speed-grind them even faster.