"standard", "thinking" and "Pro"? what are they? what usage do they cost?

In the past, MEMO allowed user to choose the models, but now there are only "standard", "thinking" and "Pro".

1. What are they?

2. what are the usage cost of using them?

3. In the past, there was a price guide for using different functions and models. Now it disappeared. what’s going on?

P.s. Background: I’m a paid user.