Besides how much money would the average user be willing to spend daily on such a website? $1? $2? That already seems like a lot to me. Compared to the amount of money being poured into advertising or politics I don't see how the balance could hold. Besides couldn't you recoup a lot of your investment in a voting ring if later upvotes partially pay for earlier ones? Especially due to the positive feedback that popular posts are more visible and therefore tend to become even more popular? And even more so if people are incentivized to vote on quickly rising posts in the hope to make money?
From a game theory standpoint it doesn't seem workable at all to me, at least if your objective is to promote insightful and interesting content over memes and pictures of naked ladies.
The cost?
Let's assume their content is essentially an ad that has no value to anyone on the platform. To get to the top, they'll need to outpay a whole community of people who are incentivized to upvote more interesting content.