As a casual player with limited funds to play or gamble, I've learned from observing and from my Chaos Legion pre-sale/general sale experience that it is way cheaper to purchase individual cards than buying packs to build your deck.
That is why I am skipping Riftwatchers and will closely watch in the coming days the prices of Chaos Legion Reward cards that will be out of print soon! I'm anticipating for prices to go down as sales from these cards can be used by those purchasing RW packs.
Personally, I'm stacking on Pelacor Conjurer, Pelacor Bandit, Uraeus, Venari Bonesmith, and Djinn Oshannus because I find them useful from Bronze to Gold. I'm not too sure how they perform in higher leagues but I can imagine Uraeus's poison and Oshannus's Phase and Forcefield can bring about one's victory.
The below table shows the percentage printed (from Kiokizz) and the 4-week average price per BCX (c/o 
We will find out. Very soon.