Like compound interest, constant acceleration is powerful. 10/m/s/s gets you to 30,000 m/s in 3,000s. That's .1c in less than an hour. The energy required is mv^2, m being the mass of your vehicle, and you can annihilate anti-matter to get, theoretically, Mc^2 of energy out of it. That means you can get to .1c with M=mv^2/c^2=.1^2 or 1% of your vehicle mass of anti-matter. That's a small enough number to leave a lot of wiggle room.

(Much smaller, and more realistic, accelerations are possible over longer periods of time, but require using the use of relativistic equations of motion.)