So let's pretend it's like this:
Black Orchid - 5$
Chief Thunder - 5$
Cinder - 5$
Fulgore - 5$
Glacius - 5$
Jago - FREE
Kim Wu - 5$
Maya - 5$
Riptor - 5$
Sabrewulf - 5$
Spinal - 5$
TJ Combo - 5$
Tusk - 5$
If that's all the characters they have then that's 60$ for the full game which is reasonable I guess. (then again, I'd rather not have to buy every pieces of the game separately)
If they have 4 or more new characters then the full game price will be 80$ or more and that's when it starts getting pretty expensive. You know, for something that should've already been available from the get-go.
Actually, this idea is both sad and interesting. Imagine if Injustice was 100% free and you only had to pay for the characters and stages you cared about/wanted to main. I would've probably only paid 10-20$ instead of 60$ which sounds like a pretty sweet deal for such a fun game.
Players willing to spend 80-100$ for the full package can do so, while cheap players like me can still play and enjoy the game for a fraction of the price.