Here's the thing with pay scaled to cost of living, it means things like pension contributions, ability to save, any property you purchase, are also scaled. There's a reason so many people flock to expensive cities early in their careers.

Very early stage startups might be able to move around Europe for a short period for cheap rents, you're going to be much less able to recruit staff (i.e. non-founders) to move from the West to Slovakia (as mentioned) to work for Slovakian wages.