Perhaps you should add different payment levels like Steem Fest:

**Monthly Plans**

There is no difference in the service offered in each plan.
The support plans show support for the service and help
cover costs for it's development and maintenance.

* Regular Fee: 0.002 SBD (0.001 SBD to @steem-interest)

* Support Fee - Bronze: 0.010 SBD (0.009 SBD to @steem-interest)
* Support Fee - Silver: 0.100 SBD (0.099 SBD to @steem-interest)
* Support Fee - Gold: 1.00 SBD (0.999 SBD to @steem-interest)
* Support Fee - Platinum: 10.00 SBD (9.999 SBD to @steem-interest)

This way the cost is low for users that don't have much to give, and those with a lot can support with more. :) You could list platinum supports on a separate page to show how great they are! lol