Increasing prevalence of price discrimination It seems to me that the variation of prices for similar or identical products has grown over the last decade. A few examples:


On major air routes, price differences between low-cost and traditional carriers are extreme.
Retail sales appear more frequent and significant than ever.
At a grocery store, on any given day, it seems like some 30% of products are discounted. And I have received up to seven non-negligible coupons (for future use) even when making negligible purchases (under $5).
"Deal sites" like Groupon (and a thousand others) have become prevalent.
Single consumer electronics items are released as many different versions (with many different prices) with only slightly differing specifications.


All in all, it just seems like companies are getting more sophisticated (and more aggressive) about extracting as much of each consumer's willingness-to-pay as possible. This begs the question:


  Can you think of any data that could be used to quantify the increase
  of price discrimination across time?


Note on edit: I originally asked about welfare considerations also, but found a fantastic answer to that question here.
For current data, you could use a scraping program to collect data from firms' websites. This was the approach taken by a recent paper for airline pricing, so it would definitely work for your first example. In general, it should work for any market that has a significant online presence with universal price quoting. Retail sales should more or less satisfy that description. Grocery stores too nowadays, at least the big ones. See the paper cited for more info on its methods.

But, as your question pertains to the evolution over time, you'd need past data as well. Have a look at The Billion Prices Project at MIT and Harvard. http://www.thebillionpricesproject.com/datasets/

Williams, K. R. (2017). Dynamic Airline Pricing and Seat Availability (Cowles Foundation Discussion Papers No. 2103). Cowles Foundation for Research in Economics, Yale University. Retrieved from https://ideas.repec.org/p/cwl/cwldpp/2103.html