Consumers, by definition, pay the price. The case of monopolies, cartels and other antitrust issues can be especially relevant, particularly when the offending entity supplies consumers directly.
A central tenet of Capitalism is that a monopolized product will be more expensive, less durable, and often just plain not as good when compared to a freely-available product. The free market ideology sees monopolistic behaviour as some weird impediment to competition leading to market inefficiency. This despite the fact that monopolists seem to grow under the freest of free markets. But that's material for another writeup. Antitrust legislation aims to return market efficiency by removing "anti-competitive" behaviour. A company or group of companies with too large a share of their market will be banned from performing certain actions which aim to reduce market freedom.
In many fields, it isn't working any longer. In the USA and internationally, Microsoft are forcing some very problematic products on the public. Supermarket chains are edging out open-air markets and many grocery shops. Few recording artists are promoted by the (few) companies who set the rules of the music market, leading to less musical diversity. Most recording artists are paid a pittance. Much the same occurs for film.
In my country, the 3 cable television companies set up a few years ago (under the usual guise of "free markets") formed a cartel from day 1; now they are all set to unite into a single company. Their "competitor", the Yes satellite broadcaster, offers a surprisingly similar product: almost exactly the same channels, at almost exactly the same price (a bit higher, because they sell larger packages of the same). They have different digital TV movie channels -- but the same films are shown on both! Unsurprisingly, neither company has exceeded its minimal investment in local production.
The banks all charge exactly the same amount for actions performed, and offer the same savings accounts. Smaller banks offered somewhat higher rates, but they accounted for a tiny percentage of all savers -- and 2 of them went under this year, after the major banks let them fall. The claim is that the rates are exactly the same, because all participants in the markets have reached the optimal point of efficiency. If you believe that, you probably don't need a bank, you can finance your needs by renting your teeth to the tooth fairy.
Why isn't the regulator doing anything? Because antitrust doesn't apply to consumers!
(ONLY) the competitors, the monopolist or cartel, and the state, but not the consumers, are parties in an antitrust case. When the US DOJ and some states brought the latest antitrust action against Microsoft, they were acting to defend some of Microsoft's competitors. Unfortunately, while giants like Netscape, Sun, Oracle and friends may have legitimate grievances against Microsoft, these aren't the same as the consumers' grievances.
The only way to express consumers' problems in the current setting is to have a corporate champion for them. And after many years of domination by a small group of huge companies, there is no financial backing for any company which will deliberately seek self-destruction to prove the consumers' points. In fact, it would be probably be illegal for any publically-owned company to act in a manner which threatened its own stability in order to be able to seek anti-trust remedies against one of the giants.
Despite being the largest segment in many markets, consumers are by now completely out of the loop. They cannot realisticaly refuse the offered services.
Few people can take the extra time off work to buy at an open-air market (the chains have the organised money to build huge parking lots). The only way to avoid satellite and cable TV is not to watch TV (the older cable TV equipment ruins reception, and the broadcast channels aren't that good over here).
Linux isn't ready for the desktop, no matter what starry-eyed enthusiasts claim, and free office programs will have a hard time competing with closed-format and changing-format proprietary office programs: consumers have to be able to read official forms and documents from their employers (supplied in MS Word format). Large organisations won't switch until they can buy full support for both systems, at least for the transition period. The monopolist won't allow any large support organisation to support its competitors. And the support organisations' bread is buttered firmly on the monopolists' side.
The banks are the worst case: Everybody has to have a bank account, even to get paid at the end of the month and to pay bills. Unfortunately, bank accounts are only supplied by banks, and the banks have a highly effective cartel in this country.
And any antitrust action by the regulator only works for a competitor or participant in a related market, not for the consumer. Their interests are rarely the same. In the Microsoft case, it is highly unclear if any of the competitors showed (at the time of the complaint and trial) any interest in breaking the "upgrade cycle" of hardware and software that modern proprietary software forces on consumers. The settlement reached may have helped some competitors, but it did nothing for consumers.
Consumers have no case under the current system, particularly not for required or "required" goods. They usually cannot organise to create competition where there is none. They cannot buy cheaper from the cartels (larger organisations have somewhat more bargaining power than individuals, even in unfree markets). And they cannot seek legal remedy, because the law works vicariously, granting consumers refuge from monopolists and cartels only by helping the competitors of those bodies. "The consumer" has not (yet?) a separate legal status. Can modern states accord consumers a much-deserved legal status?
Much work continues to be needed on consumer rights in the modern world.