Prusa is a very FOSS-friendly manufacturer. Their entire slicer and the firmware for all of their printers are free and open-source. And they make really high-quality 3D printers. With 500€ you should be able to get the Mini, though getting the larger flagship MK4S may pay off more in the long run.
Blender can absolutely be great at creating precise geometry, one just needs to know how to properly use the tool. Yes, the workflow will be much different than in other CAD, but principally, Blender is just as good as any other, or even better due to a more extensive development history and greater degree of maturity.