Protectionist mechanisms exist in most economies, whether overtly or covertly, but it is certainly possible for a non-European to work in Europe. Many millions are doing so right now! The primary hurdle is the right to live and work in Europe, which is ususally a matter of heredity - and is normally covered on the Embassy website of the country you are interested in. The process of converting your FAA licence to JAA isn't cheap or easy, but it's not as difficult as some would have you believe!
As for pilot remuneration, in western Europe it's generally (but not always) true that pay is better than in the US in the early years of a career. On the other hand, $150K for an A320 captain is a little more than would normally be expected here. As
XL5 says, the comparison isn't straightforward - issues of tax, cost of living, terms and conditions beyond salary (pension, healthcare, etc) all need to be taken into account.
www.ppjn.com has fairly accurate information about specific airline remuneration in Europe and elsewhere. Tax rates are normally found on national government websites. Cost of living comparisones are more difficult to establish accurately, but it's safe to say that western Europe is considerably more expensive than most of the USA.