That is why I think paying for a self hosted version would be a good option. I would do the following as you had 4 donator levels...
Free: 5 rigs statistics shown
Donator (Tier 1): 10 Rig statistics
Donator (Tier 2): 15 Rig statistics
Donator (Tier 3): 20 Rig statistics
Donator (Tier 4): License for Self Hosted Or a 1 time $100 cost.

Donator Levels are calculated using the average donation for the last 3 months.