Some cheap purchases quietly commit you to an expensive supply

The machine is not always the product

A number of household items are sold at prices that seem too generous for what arrives in the box. Printers, coffee machines, razors, water filters and various cleaning devices share a pattern: the device is affordable, and the thing it consumes is not. That is not a coincidence or a pricing error. It is a deliberate structure in which the first purchase is a way of acquiring a customer for the second one.

The mechanism only works if the consumable cannot easily be bought elsewhere. Proprietary shapes, electronic recognition of a cartridge, or simply a fitting that nothing else matches all serve the same function, which is to make the machine and its supply a single commercial arrangement rather than two independent markets.

Once that arrangement exists, the price of the supply is not really constrained by competition in the way the price of the device was. The comparison a buyer makes at purchase is between machines. The comparison they cannot easily make afterwards is between suppliers.

The real price has two parts and only one is quoted

Working out what such an item costs means adding the purchase to the supply over the period the machine is likely to be kept. Take an illustration and treat every number in it as invented for the purpose. A device costs 80. Its cartridges cost 30 and last two months. Over three years that is eighteen cartridges, 540 of consumables, against 80 for the machine — so the headline price is under a seventh of what the household actually spends.

Set that against a competing device at 200 whose supplies cost 12 and last the same two months. Three years of that arrangement is 200 plus 216, or 416. The dearer machine is the cheaper decision by a substantial margin, and nothing on either box would have told you so.

The arithmetic is elementary. What makes it rare is that it requires two pieces of information — the price of the supply and how long a supply lasts — and only one of them is printed anywhere near the machine.

Consumption is not fixed, which breaks tidy estimates

The second number is the difficult one, because how long a supply lasts depends on how the thing is used. A printer used for occasional documents and one used for photographs consume at wildly different rates. Manufacturers quote yields under standardised conditions that are unlikely to describe any particular household, and those figures are not dishonest so much as measured against a test rather than against you.

There is a behavioural wrinkle too. A cheap supply tends to get used more freely than an expensive one, so the household with the economical machine may consume more of it. That partly erodes the advantage, though rarely all of it. It also means the miserly rationing that an expensive consumable produces has its own cost, paid in a machine that gets used less than it might have been.

The honest version of the estimate is therefore a range rather than a figure, based on a few months of your own use if the machine is a replacement for one you already had.

Third-party supplies are a real option with real caveats

Where compatible supplies exist from other makers, the arithmetic can change sharply, and this is precisely why so much design effort goes into preventing them. Quality varies, some machines refuse to recognise them, and using them may affect what a guarantee will cover — a point worth checking rather than assuming in either direction.

The availability of alternatives is itself a feature worth weighing at the moment of purchase. A device using a common, widely made supply carries a different long-run cost profile from one that will only accept a sealed unit from a single source, even if the two look identical on the shelf.

It is worth noticing when a product category has moved from open to closed. Where a standard fitting once existed and has been replaced by something proprietary, the change is usually about the second purchase rather than about performance, whatever the accompanying explanation says.

What the pattern is good for, and where it genuinely helps

None of this makes the model illegitimate. Spreading the cost of a device across its supplies puts capable machines within reach of households that could not or would not pay the full price at once, which is a genuine benefit and not merely a rationalisation. Someone who prints twice a year is better served by the cheap machine and the dear cartridge than by the reverse.

The pattern only costs a household money when consumption is high and the purchase was decided on the headline price. Heavy users are the ones the structure is designed around, and they are the ones for whom the alternative arithmetic pays best.

So the practical point is narrow: before buying anything that eats something, find out what it eats, what that costs, and whether anyone else is allowed to sell it. Circumstances vary and none of this is guidance about a specific purchase, but the missing number is usually the one that decides the outcome.