This is only of limited usefulness if you want to buy a new mini PC (rather than specifically a used unit from eBay). For example, many current fanless models are not listed. Just searching for “fanless mini pc” on Amazon.com gives many more (and some cheaper) results.

This might be a task for an LLM-supported scraper looking at a number of online marketplaces, retailers, and manufacturer sites. Then, conversely, you could link to matching eBay listings. It would also need a mechanism for users to submit spec corrections.