Let's assume you are the paid upvote bot. I think your upvote is worthy $0.07. I buy all your upvotes, so on daily basis I get $0.70 on upvote value. That will be $255.5 power year. Which results in APR of 24%. And then I forgot to take curation rewards into account, cause I now have about 25% loss.

I guess this is Pretty close but not a perfect calculation. But it looks like you didn't get any decent calculation so far.