Let's examine the case of Poland. GUS (Central Statistical Office) reports 4473 PLN as the average gross income in Poland in September 2017 (or $1234 / €1058 / £935). However, these figures are:
1) Average (in case of Poland highly inflated by outliers working in few highly lucrative professions)
2) Only include companies employing 10 or more people (or 4.3% of all companies in Poland - yes, that's right, 95.7% of employers are not included in these figures; therefore they only include less than 60% of working population)
GUS also publishes mode (the most frequent) salary figures; the latest one I found (it's only published every 2 years) was 2469 PLN gross or 1786 PLN net a month (or $492 / €422 / £373).
Let's take Warsaw as an example (the city with by far the highest income in Poland). Average gross salary of 5699 PLN goes down to 4037 after tax. Average rent for a flat under 38 sq meters is 2142 PLN (if you want a flat 60-90 sq meters, be prepared to pay 4104 PLN a month, or more than your average wage). Based on my visit in Warsaw earlier this year, I estimate the cost of food to be roughly equal to that in the UK, so ~500 PLN a month. Therefore, with rent and food alone costing about 2/3 of net salary, I don't see Poland as a place where you can accumulate quickly. For comparison, living in the UK and making less than the average wage, I still save 50% more a month than an average person in Warsaw earns after tax. Yet, UK is below Poland on the list.