In the museum you have the option to pay what you can?

Saturdays from 5:45 pm. You pay what you want. Keep in mind that they close it at 7:45

Only one day a week they sponsor the tickets, and you can give what you can. The other days you have to give the full rate.

Only one day a week. Last year I think it was Saturdays. However, you can check that information on the museum's website, which is updating it.