Really depends on the distance and expected acceleration. You would be surprised. With Hohmann orbits, well those are designed to use minimal reaction mass. It's still a huge proportion. To really get around even the solar system you really want constant acceleration and ultimately 1 G acceleration. Even at high ejection velocities that's a lot of reaction mass.

I won't vouch for the math, but I remember reading that even with a 100% mass conversion drive (the ultimate) a ship would use approximately half of it's mass to make a round trip to nearer stars at 1G.