A big part of the reason that it’s so expensive to send objects into space is that in order to get them there, we currently use messy, chemically-powered rockets that shed pieces all over the place on their way into orbit, and then smash themselves to bits on their way back down. A much more cost-effective (and elegant) solution would be a reusable single stage vehicle that goes up and comes right back down intact and ready to be refueled and reused.
To accomplish that, a more efficient source of power is needed. Rockets that have to haul their own fuel and oxidizer just aren’t going to cut it.