What is the minimum and maximum bid for each ad format?

Each ad format has different minimum and maximum rates.
You can place your bid in accordance to the suggested rate card, Which you can also find on the panel: http://ad-maven.com/Recommended%20Rate%20Card.html

Push Notification CPC:
Minimum: 0.003$
Maximum: 2$

Popunder:
Minimum: 0.0002$ (Translates to 20 Cent CPM)
Maximum: 0.05$ (Translates to 50$ CPM)