I think 30-35% ish ROI is a decent winrate for SnGs, so if you entered 10, spending $10, you'd win $3 - $3.50 ish?

Those $1.20s are so soft though I'd be surprised if a decent player couldn't hit a higher winrate.

Winrate is proportional to game softness obviously so once you get up to like the $100 SnGs, i think 10% becomes decent.