As others have stated, you don't "buy ships" - ED is not a "pay to win" game. What you can buy is paint jobs and other cosmetic, non-game-performance-affecting add-ons, which you can then apply to ships that you already own in-game. If you don't yet own one of those ships, then you have to buy that ship with in-game credits, same as everyone else.
Example: I recently bought a Chrome Type 10 paint job during the recent Christmas sale. I didn't own a Type 10 at the time, and couldn't buy one anyway because I was out in deep space exploring, 10,000 LYs from the nearest shipyard. But when I finally did make it back to the Bubble a month ago, I went and bought myself a Type 10, and then applied the chrome paint job to it.