2D real-time space exploration / trading / fighting game. The main draw are the space battles. $15 , I raised my definition of cheap just to include this one!
There is an actual storyline with characters and some choices, which you are mostly free to ignore as you colonize planets and earn money from missions. It might be impossible to get through the game as a pure trader with no fighting.
It has been in “alpha” for like 13 years, seems to have a new release every year. It’s very stable, with a large modding community and active discord.
I do love Starsector. :) It’s basically Mount & Blade in space with amazing ship combat