In fact, you can get a professional quality model for as little as just over £10 (not including shipping costs). The linked model even comes with a special noise-reducing microphone included in the price.
Elsewhere, Amazon.co.uk has earpiece and headset deals for as low as £6.00. These won’t be top-end products, obviously, but they are unlikely to let you down either.
As with all things, it depends on what uses you have in mind. If you are unsure as to exactly what your needs are, then it is wiser to spend a little extra (we’re not talking a bank-breaking amount, after all) than it is to buy the cheapest model, saving £7 - £8 in the short term, only to end up disappointed with your final purchase.
You can get a ‘good’ (as in, generally reliable ‘all rounder’) earpiece for £10 - £20. These earpieces aren’t particularly flashy, but they can be relied upon to get the job done. As a general guide, some of the more professional quality pieces available will go up as high as £40 - £50. Depending on what these models are used for, all will do a fine job.
Of course, as with anything, there is a high-end and a low-end to the marketplace. However, unlike some markets, low-end earpieces do not represent an enormous loss in quality. They will work fine for basic/hobby use, but we recommend you spend out towards the higher end of the market for professional usage.
EarpieceOnline is a good place to get your earpiece from, especially since they offer free next day delivery on all their items.
Typically, earpieces are not an expensive item. In fact, they only cost a substantial amount when professional earpieces are bought in bulk for business use. However, the linked site is among the cheapest online and stocks a wide variety of different products.
Of course, all prices listed here are ‘ballpark figures’ unless otherwise stated. The sites/stockists you use may be cheaper, or more expensive, so it will probably pay to shop around a little bit.
If you are able to find any cheaper sites, then you might let us know, that way we can recommend them to other users.