Good post,
I also wrote a post about the viability of selling votes, I think that for a marketing company its easier and cheaper to buy votes from 1 big whale than to invest 500k on steem power. I say 500k because anything less than that wont get your post into the trending page.
Buying votes makes sense to me as well. As for needing $500k, I don't think that is necessary. Having enough to vote up your comments on active posts can help a lot I think to gain attention. Also, a post that hit the front page from one $500k up vote would die quickly with down vot if people thought the product or company involved sucks. On the flip side $50k might get enough attention to then get more votes that get you on the trending page for a company or product that the community thinks is cool.