So for now, it's in dA's points and Flight Rising's gems! They're both worth the same (one bit of the currency per cent), so the amount in parentheses applies to both.
I'm unable to get example images down yet, but here's the info:
Lined + flat colors, optional effects - $10 (1000)
Lined + shading, simple background - $15 (1500)
Lineless - $20 (2000)
Shaded lineless - $25 (2500)
Bigger piece + better shading, effects, border, background - $30 (3000)
Everything is a bust by default, making it waist-up adds $2 (200), making it a full body adds $5 (500). Additional characters adds $1 (100) apiece.
I've only done one commission so far, which was a $5 bust for my friend Jam: