We just had a great discussion about some of the different sandpapers available and this Jonathan Katz-Moses YouTube sandpaper test was posted. If you haven't seen it it's very good and he used a robotic arm and pneumatic sanding head from ATI Automation in Apex to do the sanding. It applied a precise amount of pressure and motion so it's a fair comparison. The "cost per gram of sawdust" and "total grams of sawdust per sheet" are good ways to look at it instead of only comparing per disc cost. Here's a link to the video and to the results.
The Great Sandpaper Showdown: Top 3 Sandpapers For Woodworking In 2021