I'm not moving to Poland to become rich
Nobody said anything about becoming rich. But moving to a foreign country without being able to save up for a rainy-day fund would be very unwise. Pretty darn stupid, actually.
Salary for entry level programmers in my country is around 1300 eur, but cost of life is almost double of that in Poland.
Remember that cost of living for you as a foreigner living in Poland is going to be a lot higher than for a Pole living in Poland, for the reasons I outlined above. You're comparing apples and oranges. The cost of living to wages ratio may well turn out to be lower in your own country.
I think that Poland is the most logical choice.
Extremely unlikely. There are far better opportunities elsewhere, both for employment and for self-improvement, which should be a major concern at your age. I cannot fathom how you can imagine that working in Poland for peanuts is a "most logical choice". It might make sense if you're making more than just peanuts (4000 PLN net), but even then, I would hardly call it the most logical choice. The most logical choice would be to beef up your qualifications, whether you are working or not, and you are going to have a hard time doing that in Poland.
I suspect that you are romanticizing. You had a fun time on Erasmus, which is great. But you're in the working world now, and the rules are fundamentally different. What qualified as fun before may qualify as unbearable drudgery now. I did exchange programs to Germany and Denmark when I was a student, and had a wonderful time. I cannot imagine living under such conditions now, though. When you enter the workforce, your priorities and standards change radically. The ones you seem not to be taking into account are building up a rainy-day fund for emergencies and continuous improvement of your qualifications, neither of which you will have opportunity to address in Poland unless you are getting paid quite well.