At that site, orphan sponsorships are about $400-$600/yr. I'd rather not do monthly because if people didn't meet their commitment then others would have to make the difference and might not be able to do.
Tsunami donation can be any amount.
Other organizations have sponsorships, I don't know what organization might be best. I sponsored orphans through Childreach for a decade, they're a non-religious organization, but they're cheaper.
It all depends on what you want and how much money we're talking about that people will commit, etc.