between one buyer with fairly limited funds and few large corporations with extensive funds
Which is the same as saying that every vote is transferred between one voter, with very limited knowledge and political awareness and a few politicians with extensive power because politics is what they do their entire life.
Democracy is, in many practical sense, a market for votes. One which is way less regulated than the one for goods and services
Well, that's not our democracies work. We don't let people vote every law by referendum, that would be spreading power as much as possible.
In ancient Athens it was common, as was common for judiciary decision to be made by 3-4 hundreds people drawn at random. But that's something almost universally considered stupid now, we have a judge, who we consider an "expert" in law.
By your definition, we don't live in a democracy, on the contrary, democracy is extinct on this planet