As far as I am aware there is no need to have anywhere near that level of hardware investment to process the blocks needed to be a top 20 witness. Currently only one server can be used to fulfill the role of a witness at a time and therefore there is a practical limit to how much money can be spent on one (rental). It generally makes much more sense to rent hardware than it does to buy it for such purposes and with things as they are (I am open to being corrected) it should be possible for medium to high end standard servers to handle the task at such throughputs. It is possible to rent such hardware at prices that are well within the reach of many if they want to get started in that role.

I previously explained a concept of altering the reward curve for witnesses that would potentially make any challenges here easier to process:

https://steemit.com/steem/@ura-soul/can-we-improve-steem-s-future-by-re-distributing-witness-rewards