Am I likely to do any better than that by buying a local SIM in Europe??!!
a basic SIM card for a pre-paid number here in Poland is in the range of couple of zlotys (PLN) I guess it is similar in the Czech Republic - you can buy it in every news agents (or whatever it is called in American English) - the top-up cards (or rather coupons) for those pre-paids are also ubiquitously available (again all newsagents - newsagents are often in kiosks here) and are relatively cheap
the simplest solution is just buy a pre-paid number in Czech Republic when you are there and then repeat that in Poland - it costs peanuts - as for activation of the number I can't recall to be honest - I have bought mine years ago and I just simply don't remember how it is done - if there are some instructions in Polish (or Czech respectively) ask local people to help you (I wouldn't expect instructions in English for a pre-paid SIM card in Poland to be honest)