Without leveraging existing infrastructure, going through a spacecraft project, from definition, requirements, design, IAT, validation to operation takes decades. The spacecraft (whatever that is) itself consists of both ground- (TC/TM, land, boat, a lot of humans) and space-segments (battery solar panels fuel-oxidizer PCDU OBSW life support transponder etc etc). Say you can buy all these sensors actuators, and don't have to manufacture all the hardware by yourself, there's more than that. To verify the system works correctly you'd need to run simulations, adjust your controller and tune parameters. From pure software simulation to hardware in the loop. Then you need to build these software/hardware tools and testbed from the ground up, and of course a huge infrastructure to lock down design and test result at each phase to make it reusable for the next project. You'd need to write up the procedure of how to operate, and train both your ground-based and space-based staff.
I doubt there are enough people within this group who are able to do this, even if we assume some of the economies are willing to invest capitals into this and expect no return.