I recently went to the US and bought a Relay from eBay for 99$. When you go there in person, no taxes need to be paid.
But I bought the first Relay some time ago also from eBay, and their GSP (global selling program) is really good. Especially because they tell you in advance how much shipping AND taxes you have to pay, and I had not only this but some other stuff as well shipped to me and I never had to go anywhere to pick it up and never had to pay anything additional. So for buying to the EU at least I can very much recommend it.
You'll recognize GSP items if it says something like "includes customs clearance and international shipping with package tracking" (in your language) and they give you an estimate of the taxes and shipping on the eBay item page.
And in my experience, declaring items as gift does exactly nothing, because it doesn't matter - you're bringing goods into the country and you have to pay taxes for it, no matter whether it's a gift or not. And finally, according to http://www.dutycalculator.com/countr...g-into-Poland/
you don't have to pay anything if the total value is below 150 EUR - which should be enough to get a used Relay 4G.