The two major companies are
Sevenstar Yacht Transport: Sevenstar - Yacht Transport over Seven Seas | IJmuiden
(yacht put on a ship with a crane like a container)
Dockwise: Home :: Dockwise :: Exceptional Transport Management
onto the ship)
If you're willing to wait until the last minute (4-2 weeks until scheduled departure), they may have specials of up to 50% off. But on the other hand, they might not have space at the last minute, so a bit of a gamble. Also check out different departure ports
from US - prices and availability might be vastly different. For example, a lot of boats are shipped from Caribbean/southern US to Annapolis/Newport. So that stretch might be busy and expensive, but cheaper afterwards.
If you were asking in more general terms, there are also deliveries, where a hired captain
and crew deliver the yacht for you.