Links

Signal shares what it costs to make Signal:

We estimate that by 2025, Signal will require approximately $50 million dollars a year to operate (…)

Here we review some of these costs and where this money goes, [and] help clarify just what is required to fulfill the dream of privacy-preserving alternative technology, and contribute to establishing a solid foundation from which we can grow alternatives that contest tech surveillance and the incentives behind it.

(From: Privacy is Priceless, but Signal is Expensive on fhe Signal blog)

They do all this with donations, not investors.