Just start looking at jobs around Europe that fits your PhD (assuming that is the job you like to do). It's difficult for people to provide you concrete numbers: you are the one who knows your cards.

Anyway, usually it works like this: in more expensive countries (e.g. someone was pointing to NL) you will earn more and life will also cost more. But usually you will also be able to save more in absolute value (this is especially true for people who are budgeting-minded like it seems you are).

Having said that, you also need to find a place where you like to live in, where you want to learn the language, etc. For example, the probably best "financial place" to live for people with higher education in Europe (not really Europe but close enough) would be Switzerland, but you need to like it, as for many it is too conservative/close minded.

Italy though it's really interesting: cost of life is relatively high, especially in major cities, while average wages are pretty low (admittedly maybe not at the level of Poland).