The budget depends on the number of days and things you want to do. Poland is cheaper than some other places. So you can stay in hostels and work out an afforable trip. Most EU countries are easy to travel as they have good transportation in major cities. You can walk rest of the areas generally speaking.

Wrote a post about visa check it out

1-1.5L is a good budget for 1-2 week trip. If you go complete budget then you can do a lot in 1.5L. You just need to find cheap airfare, cheap places to eat, stay and you can use flixbus to travel around EU which is quite cheap compared to flight or train and stay in hostels instead of hotels and buy your food at supermarkets instead of a cafe/restaurant. :)