Most phones don't have battery that is removable. But they are indeed serviceable. The battery alone is generally about 10 to 20 usd. And depends on where you are, add the service fee. Your phone is again good for 2 or 3 years. It's really just a tiny portion of new phone consider high end phones today went up to 1000~1500 usd range.

The official vendor normally have an artificially high service fee because they want you to buy a new one instead which is much more profitable. But servicing it in third party vendors isn't that expensive.