But I don't want to sell my attention! At least not at the crappy valuation the bike advertisers offer.

Money being fungible means that one dollar is as good as another. It all goes in a big pile for the budget. In other words, you don't have to match up your revenue sources with your costs (like bikes with advertising), though this is frequently used for the purpose of trying to justify one thing or another.

Money can be moved.

From where? You might live in a flush city, with lots of extra discretionary $$ flowing around, but most cities in the US are nearly bankrupt, and leveraged to the hilt on providing basic services. This is the definition of a "luxury belief", thinking the average city can just find money and put it towards removing ads that pay for services.