From what I've heard Lisbon is about the same cost as Berlin. But the economy is worse, the tax system seems more complex and it's less accessible to foreigners. I guess the weather is nicer, but the location is worse. To legitimately compete with Berlin I think one really has to offer something special, otherwise Berlin wins by default in the low-medium cost category. Lisbon would still be on my shortlist for European bootstrap cities, but there are also at least half a dozen other cities that could be equivalent.