You sort of answered your own question -- in both examples you specifically pointed out work that you have to do in order to calculate a price -- you need to sift through Craigslist items, keep track of what you find, apply a calculation, and come up with an estimate. Same for eBay.
The work you're doing there takes time and has value, and Pricenomics is trying to capture that. I'm not intimately familiar with the company nor do I know if they'll figure out a viable business model, but I do see the intrinsic value in what they're proposing.
effort wise, it looks like search craigslist == search pricenomics, with craigslist being smart enough to limit my last search to the geographical area where I last searched, whereas pricenomics showed me the results around the country(with option to filter it down to location later).
All things being equal, the effort is the same in my opinion
The work you're doing there takes time and has value, and Pricenomics is trying to capture that. I'm not intimately familiar with the company nor do I know if they'll figure out a viable business model, but I do see the intrinsic value in what they're proposing.