Do you mean validation (cost almost nothing and is there since a long long time for EASO2FAA, just recently the other way around as well) or full license? With validation you receive a FAA PPL(based on foreign license) with some ratings, where you can top the rest. Validation:
http://www.faa.gov/licenses_certific..._verification/ is mainly paperworks and oral at an FSDO, plus a one hour practical instruction and checkflight. The oral can also be done in Europe, as there are some examiners traveling - for such look at the announcements at AOPA (but does cost some money, I heard englishman Adam House from Derbyshire charges £385 via AOPA for that). For full license all your EASA hours and theory may be taken instead of FAA's, so you only have to do the exams though.