This is all correct, but may I suggest abandoning $ calculations and using STEEM as the native and base currency.
For those paying in STEEM, it is then a simple calculation to value the upvote and the amount needed from vote-sellers. The value of an upvote is based on the official blockchain price, however wrong it may be compared to external market prices.
I also think this is a good time to ditch the $-designated rewards and show them in STEEM. Then users will also see how stable upvotes have been in STEEM.
Thanks.
RE: Fairer Price Calculation