I have been relying on the estimable Chicago Dispatcher monthly newspaper for Chicago medallion sales prices, because I could never find them on the City’s web site. Now, while trying to figure out something else, I have found the site. The same page with a different url seems to be here. It’s not clear whether this link is permanent, but one can navigate to it from egov.cityofchicago.org using Your Government > City Departments > Business Affairs and Licensing > Public Vehicles > Taxi and Limo Industry > Medallion Owners. The latest list posted, thru June 8, is this pdf, showing that on the last date reported, June 9, ten sales closed at prices ranging from $165,000 to $178,000.
Other medallion-related items: Here’s a post indicating that New York, too, is seeing continuing rise in medallion prices. And Taxi Medallion Systems do not Benefit Drivers.