No money is not speech. It's money. Putting a limitation on campaign contribution in no way shape or form limits your speech.
Really? Citizens United was about some people who made a movie about Hillary Clinton. If the government forbids you to spend money on making a film (or publishing a book, putting up a website, or buying an ad, or making a sign, etc.), they are certainly limiting your speech.
And note that even the defenders of the McCain-Feingold campaign finance law that Citizens United overturned admitted in court that the law would have allowed the government to stop the publication of a book if it was about a candidate. If that isn't suppression of speech, what is?