This will depend largely on your personal situation (where your place of residence is, EU , Poland USA etc.).
If you live in an EU country for more than 6 months, you will have to register your car in this country and pay registration fees + taxes (eg poland). there are exceptions to the general rule here as well if you live and work in diferent EU countries. So more information would be needed.
I am a lawyer based in Poland, so I might be able to help you with all legal and financial issues related to purchasing cars in Poland.
If you are still interested, please send me a private message on this forum and we might be able to help you with your case in Poland.
Archives - 2010-2019 / Law / Purchase a car in Poland without further registering it (I want to move it abroad)