Hmm, law does stop you from doing that, as you need to actually live in the place you subscribe to your plan.
Also, I'm not sure it's that cheaper in the East, I can't really find plans that are significantly cheaper than 40 GB per month for 10 euros.
50 GB in Poland is 100 zloty with Orange for example, so 23 euros.
Nothing stops you getting cheap plan from Eastern Europe and use it in west (where cost of operations are higher).