There is a flight school in Poland, the name is Bartolini Air, they have reasonable prices and I've heard only good things about them here on the forum.
Don't know them personally, only had contact via email (always had to wait a few days until my mails where answered) but besides that all of my questions where answered satisfactorily. I'm planning to do the practical part of my conversion (FAA to JAA) with them. Currently they don't offer the ATP theory course in the English language (only Polish), but they told me that the theory and the exams can be done in any other JAA member-state, it will be accepted by the Polish CAA. After finishing the practical part in Poland (Bartolini Air) you'll be issued a Polish JAA licnese.
Check also the following link, regarding - cheapest place to do the conversion:
http://www.pprune.org/professional-p...-aptl-mcc.html