There's a saying among KSP players: "Orbit is halfway to anywhere". It takes a lot of energy to escape Earth's gravity well. It takes a comparatively tiny amou

There's a saying among KSP players: "Orbit is halfway to anywhere". It takes a lot of energy to escape Earth's gravity well. It takes a comparatively tiny amount to escape the Sun's, as a sibling poster pointed out. It would be actually harder to visit, say, Mercury, as you now have to shed all the energy Earth has given you for free, in order to "fall" into the Sun's well. Voyager wanted to visit multiple planetary bodies – changing orbital parameters is not cheap. But if all it wanted was to get out of the system, burning straight out would probably be cheaper (in Delta-V terms). The closer to Earth the better, for the Oberth effect.