Actually, quality two-way radio earpieces are not nearly as cost prohibitive as you might expect them to be.
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 have earpieces at a low cost. But these obviously won’t be top-end products.
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. This will mean that they will last 4-5 times longer and save you money in the long run.
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.
If you are spending a bit more on an earpiece you might be getting some added extras that will make the earpiece last longer, for example, better plastics of the cabling that won't fray of snap and added kevlar cabling to increase the strength. Better quality speakers and mic, for improved sound so you don't miss important calls. Normally spending a bit more is more cost effective than buying a cheaper one every few weeks, also, they may help protect your hearing in louder environments.