I once had a prof take our class through the 1G acceleration calculation for getting to the galactic core. What I remember most was the amount of energy you'd need to accelerate/decelerate a decently sized ship. If you assumed a perfectly efficient engine with an anti-matter reserve you were converting to energy (via E = mc²), the mass of anti-matter needed was something on the order of Earth's mass. And that's why when people talk about intergalactic exploration in our species' future, I don't get too excited.