You can buy all kinds of knockoff (and surprisingly high-quality) straps on Amazon, for $50 or less (many of mine were about $15).
Apple, on the other hand, charges eye-watering prices for fairly basic straps.
All that said, the last few years, I've just been getting the stainless steel variants of the Watch (I currently have an 8), and use a metal band that I got for about $25[0].
The Apple version of a similar band is ... slightly more expensive [1].
[0] https://www.amazon.com/gp/product/B09JWLYLG5/
[1] https://www.apple.com/shop/product/MUHJ2AM/A/38mm-silver-lin...