Euros, actually. Does seem steep. But still, small government guy that I am, I nevertheless want us (Americans) to build something better and more powerful, even if it costs more.
For instance, I'd LOVE to see us build a space-based optical interferometer, perhaps a few million miles across. But still doable with today's technology, not too expensive and serviceable. With such a telescope, iirc, we'd not only be able to image small planets out to several hundred light years, but rivers, lakes, forests and perhaps, animals, if those things exist that close to us.
But a billion dollars??
Well, that does include a mountain in Chile!