For reference, the low-tech solution to getting a lot of delta-V is the Orion drive, which involves pointing a nuclear shaped charge at your ship and setting it off so that you can rocket-jump on the nuclear explosion, and then repeating this process every second until your ship is going fast enough.FTL is like magic: outside of a few known tricks, it works however the setting needs it to work, because we don't have any basis for it in reality.
That being said, if you are talking hard sci-fi space travel, the problem isn't powering your ship's equipment, it's having enough stuff to throw out the butt-end of the ship to make it start and stop, you should be asking how they get ships across a solar system in a mere month or two with chemical or ion thrusters.
And then when you get close enough (possibly only halfway) to your destination, you turn around and do the same thing in the other direction until you stop relative to your destination.
And then when you need to come back, you do step one again.
And then when you get back home, you do step two again.
And this can theoretically make for an economical round-trip time from Earth to Venus and back of 19 days or so.
EDIT: But even with that, 75% of your ship's initial mass will be nuclear shaped charges, and I suspect that it may only be that low if you reload your nukes on Venus.