Maybe he is setting prices so it becomes cheaper for them to raise their own Army to the task, rather than renting American mercenaries for a relative song.
I think he knows they won’t pay 150% of the cost and is simply signalling that he’s willing to settle for payment of all or most of the cost with no premium. In other words,he is negotiating.
You are half right about the renting of American mercenaries. The problem is, to quote the guy from the Rock, “Mercenaries get paid.” We don’t.
The British had it right in the 18th and 19th centuries, when they employed the “Golden Cavalry of St. George”: they would use their navy to control the sea, but use their wealth from their empire to pay powers like Austria, Prussia, or Russia to do the bulk of the land fighting against France and its allies. We do some of the same these days, but not when it comes to Europe. Now, the Prussians use us to protect them from the Russians, and we bear most of the cost for doing so.