There are some ok ones on Aliexpress. I got a very basic and cheap one from a brand called ESR on that site
As a warning, some of them such as this one take up the Apple Pencil’s space so aren’t compatible with it (unless you’re miraculously genius at cutting a chunk from the side off) , but I’m not intending on using the pencil so I was ok with it (but be careful about that if you are)
Overall however these are probably a better deal than the ones that Apple offer