In short costs circa $20,000 - and has been asked many times before on this forum and jetcareers.com
Required:
ATPL groundschool - circa $5000 including exams
JAA CPL can be done in USA - training as required ; normally a good estimate is $2000 + skills test of approx $1500
JAA IR Conversion ; 15 hours MUST BE DONE IN JAA STATE and around $10,000 including exam fee.
Conversion is not easy and many students go over the minimum hours.
Unless you have the right to work all ready in Europe it is not worth the investment.