I don't really know where they get their data and the overall picture might well be right but e.g. the rent index within Germany is quite dubious: In their list, Frankfurt and Cologne have a lower rent index than Berlin, whereas I think the map on immobilienscout24 looks a lot more believable[1]
I don't have original or better data but let's carefully say that from the anecdotes that reach me it would be useful to study what rent you would have to pay realistically (for an apartment and for office space) as a non-local coming to a given city. Specifically, as a start-up founder or engineer, you would most likely not want to live in the cheapest neighborhood, independent of if it's New York, Sofia, Warsaw, or Berlin.
tl;dr Most eastern European capitols might be a lot cheaper than Berlin but the linked data should not be trusted blindly.
I don't have original or better data but let's carefully say that from the anecdotes that reach me it would be useful to study what rent you would have to pay realistically (for an apartment and for office space) as a non-local coming to a given city. Specifically, as a start-up founder or engineer, you would most likely not want to live in the cheapest neighborhood, independent of if it's New York, Sofia, Warsaw, or Berlin.
tl;dr Most eastern European capitols might be a lot cheaper than Berlin but the linked data should not be trusted blindly.
[1] http://immobilienbewertung.immobilienscout24.de/karten/