If the trickle down percentage is equal then the problem in the US is extractive labor unions; if US workers get a smaller percentage of the billing rate then the problem is extractive behavior by contractors. These problems require different solutions, so any attempts at cost control would need to determine which of these possibilities is in force.
US healthcare costs will also almost certainly feed into higher employee compensation for American workers. European employers will be paying into health care in some form or other (either through taxes or private insurance) but overall healthcare costs in Europe are far lower than in the US.