This site performs a twice-daily scan and plots out thousands of MiniPCs from Amazon and eBay, according to their prices and specs. You can adjust the horizontal axis, or the color code, in order to search several dimensions at once (e.g. CPU Performance vs Graphics). See my blog post for more info.

BTW it of course uses affiliate links - scraping and parsing all these PCs from Amazon and eBay every day isn't free!

You're gonna need to enable Javascript though, sorry.