The achievement is called "Absolute Zero" with the description "You know we're running a business, right?"

In order to unlock the achievement you must build a ship which nets you a profit of $0

For the most part, this achievement is actually really easy. It's just that the average space engineer doesn't think "I need to make absolutely no money on this ship"

The best time to do this is in late game when you generally have the parts you need and not much of a need for money. When you get a contract you can build the ship however you want, throw some cool tractor beams on there! Wren wants a nice little cruiser? Give him a giant plasma cannon! The Outlaw wants to hunt down bounties in an epic gunship? Let em have some rainbow engines! Garbage Girl needs a trash compactor? Here's 19 nuclear reactors, bestie. You get the idea.

If you're a bit of a lazy engineer then feel free to make a normal ship with the normal requirements then add on tons and tons of extra stuff. Wings, cargo, command, passenger bunks, etc. If it's cheap and doesn't have secondary requirements then you may as well throw em on until your profit hits that nice round 0.

Here's some ships I made as examples much to Selene's disapproval

As mentioned by Tiwaking in the comments, some contracts will force you to end with 4, 6, or 8 credits. This means that unfortunately you're going to have to make profit no matter what. A true shame.