I believe I understand your point. In an important way, I don't disagree. A financial transaction is an inherently honest communication between buyer and seller - the clarity of the signal that buying and selling sends is the mechanism behind the efficiency of free markets. I agree with this. Is it close to your point?
My point is that there's not much value in this honesty beyond the efficiency of markets. It can't be used to express complex ideas, to make logical proofs, or create art. It may be honest, but it is not truthful.
Moreover, though communication in free markets is honest, it does not constitute "speech" in the sense of free speech. It is what it is: trade. Not all actions, even if the action expresses the actor's unique will, are speech.
Markets should not be optimized on the idea that participating in them is speaking freely. Free enterprise is its own good, separate from free speech, and with its own ends. Confusing the two grants undue protections to those with the ability to "speak" loudest via a financial transaction. Confusing the two allows us to turn our political civitas into a parody of a free market, openly allowing the will of public officers to be bought by the "speech" of the rich.