nice, though I think it would be good to have different design, instead of just the same coin shape.

10$ -> coin
100$ -> "gold" bar, or maybe stack of coins.
1000$ -> steemit branded diamond XD

But if the goal is to have consistent design for the same kind of badge, then your proposition is better.

But add some sparkles to the higher tier badges XP

In any case, good work !
I really like the idea of having a bit of gamification on eSteem !