Seems a bit expensive. I haven't flown transatlantic for a few years but most airlines used to consider a bike as one of your allowed two pieces of check-in luggage, each of which could be up to 32kg in weight. Remember that flights to and from North America use the 2 pieces system rather than the 20kg system that most other international flights use. So you could have your bike as one piece and a large bag of some kind with all your panniers and other luggage in it as your other piece.
Things may have changed in the last couple of years though with the general tightening up of baggage allowances. Best to check with a wide range of airlines.
I doubt if any other method (excess baggage companies, shipping companies, parcel companies, etc) would be any cheaper than he has been quoted already.