there is completely different regulatory landscape and thus price to enter the game. Any fission work would involve radioactive elements from the start. Licensing and approval on all the levels from federal to local require investments and political power on the scale well beyond ...
An even if you manage to develop and prototype the fission reactor, the deployment is still and even more subject to that approval problems.
The nuclear fusion work, as long a it is deuterium based (tritium can be bread during the process) and no dual-purpose equipment is attempted to be bought (like very large power lasers or extremely short-impulse discharge devices) can be conducted in your garage ... well until you start getting real neutron flux (or gamma flux before it if you're going fusor way) - either you and your neighbors get serious health damage/killed or you start installing protection from the flux - that would involve money and questions on why would you need so much of boron concrete :)
The fission startups out there (most notably TerraPower) do all of their work in silico, and that's representative of fission reactor design in general. Fission reactors aren't prototyped, they're simulated exhaustively, approved, and then built.
You're right, though, that securing the materials for a fusion prototype is less legally fraught.
An even if you manage to develop and prototype the fission reactor, the deployment is still and even more subject to that approval problems.
The nuclear fusion work, as long a it is deuterium based (tritium can be bread during the process) and no dual-purpose equipment is attempted to be bought (like very large power lasers or extremely short-impulse discharge devices) can be conducted in your garage ... well until you start getting real neutron flux (or gamma flux before it if you're going fusor way) - either you and your neighbors get serious health damage/killed or you start installing protection from the flux - that would involve money and questions on why would you need so much of boron concrete :)