Hi, I think the cheapest 3D printer kit was in the 250$ range and the company went under. You could probably find something starting 300$.

It's nice if you have computer part lying around but that barely helps as a 3D printer is a lot of mechanical hardware. For instance for FDM machines :
- minimum 4 motors
- belts, bearings and rods
- a print bed
- a feed gear
- a hot end

Good luck