That's a lot of expense on capacitors. When we made a rail gun at school, we built our own capacitor bank with big glass cider bottles. Main problem we had was the projectile (ball bearing) welding itself to the rails. Solved by rubbing them with graphite before each firing. No idea what the efficiency was, but we lodged several bearings deep in a brick wall.

They made us dismantle it as it was unsafe - so we re-use the capacitors and made a tesla coil.