What do you mean by preparation? all the required training? or just a brush up after already doing the required EASA training that was a while ago? If the former, The first step would normally be to ask what training your EASA training organisation determines you require for the conversion process and that will tell you where to start and enable you to work out the cost difference (and factor in whatever the FAA currency is worth to you) . I think you'll find that adhoc EASA fixed wing training is hard to come by in the USA, but of course generic multi IR training is relatively abundant. And yes, IR training has to be in European airspace. And it would make sense to do the CPL in the airspace you are going to take the flight test and much easier to get an examiner in europe. Hotel car and daily expenses are going to be 200 usd a day , plus a flight and jet lag recovery time. What about Poland? seems to be the other option for CPL/IR...