[duaneb]

This is only as an employee. You're free to contract your own rate at whatever you'd like (including for free); while "salary" implies a full employment that doesn't look like the case here.

EDIT: none of what I said applies; this was in Mexico.

[nine_k]

While I may agree with some criticisms of minimum wages, there are jurisdictions that mandate a minimum hourly rate. Most of the US states are such jurisdictions.