Who pays for Citi Bikes?

So, the question is: who exactly foots the bill for all those Citi Bikes we see zipping around the city? Are taxpayers footing the entire cost, or is there some kind of revenue sharing model in place? Are there sponsorship deals or advertising partnerships that help offset the costs? And how do the costs compare to other modes of public transportation in the city? It's definitely a question worth exploring, especially as more and more cities around the world adopt bike-sharing programs as a way to reduce traffic congestion and promote sustainable transportation.