You may want to define the different amounts for Backers and Sponsors to contribute to your Collective.
To set these up, log in and go to 'edit Collective', and head to the 'Tiers' section.
Type: donation or ticket sale (for events)
Name: e.g. Backer, Backer Plus, Silver Sponsor, Gold Sponsor
Description: What reward backers at this level get or what it means
Amount: the price
Interval: Once, monthly, or yearly
Quantity: if you want the Tier to be limited (for unlimited leave empty)
To add more, click the blue "add another tier" button.
Don't forget to save your changes so they show up on your Collective page.