Are you serious ? in Ukraine ?
I make about 60k$ in Paris, and have a lot of friend making about 50k$.If Ukraine is like that, I'll be there in two months ! :)
I am totally serious a good Ruby dev with 4 years experience and really good english 4K/month is very doable. A good Senior Java dev would be 5K-5.5K (I had actually people turning down 5.5K/month for really nice remote positions).
Can't say how tax/work permits work for foreigners but for citizens they operate under Private Entrepreneur thingy and basically pay flat 3% tax.
Do you have a number for C++ ? Thanks for the info anyway :)
For C++ only know that for DSP jobs it is in 4K/month range can't say what it in general.