Supporter - How Create Paid Levels Only (No Free Level)

Hi,

Supporter seems geared toward allowing free signups, then upselling to a "Pro" or "Supporter" membership to receive additional benefits.

Could the plugin be used to create a system with only paid levels (no free level)? For example, a basic blog would be $, and upgrades would be $$?

If so, howe could this be achieved?

Thanks.