This was a lot harder than expected but i've finally reached Gold for the first time. I don't think it's possible to reach Gold without investments, especially in the summoner.
Just having a legendary card like the Ruler probably gets you to Silver II and Silver I but that leap up to Gold has been impossible for me.
Now to try and play the Life Splinter for the daily rewards which will probably knock me back quite a bit.
I probably spent around $15 improving my decks and i think it has been worth it so far with the additional cards in daily rewards and also season ending rewards.