However, if you're specifically saying you can build a working faster-than-light drive AND a fleet of starships, I suspect your economics are a tad low. If you're just saying we could build a bunch of X-33s for that much money, I agree with robur - yes you could, but why would you? Especially since X-33s are neither faster-than-light, nor can travel interstellar distances.

For my money (all two cents of it) I'd go with a 20-year plan to fund a relatively modest program to first develop an FTL drive (say, a few tens of millions per year). However, this involves a lot more foresight than Congress seems willing to have, witness their reluctance to fund SETI research.