Eve\'s PLEX, which you refer to, is not trading real money for in-game credits. It is a 1-month subscription game time code in the form of an in-game item. The credits you get for then selling it in the in-game market come not from CCP but from other players who give you their credits so they don\'t have to spend $15-20 USD that month to keep their account active.
Converting PLEX into Aurum (a second currency that is used for CCP\'s NeX store) makes it closer to what you describe, but with the market, you don\'t need to spend a single real cent to get those. In addition, the NeX only gives you clothes for your avatar, which are purely vanity as Eve gameplay revolves around spaceships. In-game credits from Aurum, like with PLEX itself, come from selling the clothes to other players.
EVE does have some Game Time Card offers that give you a ship with the couple months of game time, but that ship is identical in every way but skin to one that a day1 newbie can build with a recipe and minerals.
Regarding cryptocurrency to credits in StarMade, I\'d say no. While Eve can get away with selling vanity, StarMade\'s skin and texture setup means that option is out the window. SM is also not a subcription game, instead going the route of \"buy once and done\" once it\'s released on Steam. This leaves trading real money for things that impact the gameplay, aka \"pay to win.\"