There is cheap, which can mean so cheap they are a heap of trouble.
There is inexpensive, which may well give all anyone really needs, especially for air rifle ranges.
There is mid range where superior glass, coatings, and build, come into play.
Then there are the very expensive top end scopes, which may well be over kill for air rifle use.

Cheap is just that.
The inexpensive and mid range is where there is a heap of competition.
High end has the extreme cost that may or may not be justified for the application.

The best high end scopes can deal with very tricky light conditions that aren't really apparent at air rifle ranges. Repeatability and build quality are very high, and they generally deliver for decades. For certain applications they have their place.

In recent years there has been some excellent improvements in both the inexpensive and mid range categories. Many manufacturers are following trends and fashions more closely, as seen by the proliferation of FFP scopes over SFP scopes and more reticle designs thanks to improvements in glass etching.
Scopes make good money as manufacturing them has never been less expensive, but in a crowded market more is spent on the marketing to get them sold. Prices reflect what price the market can handle, and if anything scopes are expensive for what they are even though they can be really good. Sure a lot of the costs now are marketing, after sales service/warranties, import charges, agent mark up, VAT, and retail mark ups. Which adds a lot of costs beyond just the manufacture. However, the consumer is getting what they are asking for, with plenty of choice.

Basically decide what you want for the rifle you have, for what you envisage the combo is going to be used for. Do try and match the weight, features, and scale, to the rifle at least.