MS in finance in english at Poznan University of Economics
You have a BS in mathematics, so why are you studying generic finance instead of taking advantage of your math background to study something more math intensive and salable on the job market like financial engineering, econometrics or actuarial science? Your job prospects, lifetime earnings potential and lifetime savings potential would be MUCH, MUCH better with degrees in those subjects than in generic finance, in which there is a glut of graduates. A degree in these subjects from a excellent school with an excellent reputation would well be worth the price. Schools like LSE, Imperial College or Warwick in the UK, or any of the top math/engineering schools in the US like the ones on these lists:
quantnet.com/mfe-programs-rankings/
grad-schools.usnews.rankingsandreviews.com/best-graduate-schools/top-humanities-schools/econometrics-rankings
colleges.startclass.com/d/o/Actuarial-Science
Generally, programs in English in Poland are not considered rigorous and do not carry much weight with employers. Actually, the MAIN reason you are going to university is to make useful contacts that will help you in your future career. Your chances of doing that will be astronomically higher at any of the universities on the lists above than at any Polish university, especially since you do not speak Polish.
Frankly, studying in Poland to "save money" would be the costliest mistake you could ever make. Always make decisions based on your lifetime savings potential, not the cost of tuition.