Freedom of expression inherently includes the freedom to pay for expression. What are your expression worth if you wouldn’t be able to pay a service, cellphone/internet connection/reddit gold to express that? How is paying ads different than paying a campaigner set up a loudspeaker in the middle of a city? But then again, since twitter is a private enterprise, I fully respect their right to act on their own platform.
Absolutes don't really work well in the real world: there are too many trade-offs to be balanced and too many positive goals that are at tension with each other. For instance, and absolute right to paying for free expression sounds nice in isolation, because we value free speech. But we also value democracy, and democracy doesn't work well when an oligarchy or foreign power can use its massive wealth overwhelm and confuse the expression of the common people.