The problem with clusters is that each part of a cluster ends up costing as much as a whole HW in its own right if you want it to survive facing a machine twice its own weight.

The machining costs are doubles, part costs are doubled, material costs are doubled etc. While your system of splitting the build would work, you end cost would be much the same just across 4 people, which would be the same as building 1 robot with 4 people.

Provided all 4 machines have a consistent theme, design and looks it would have a chance. If you are careful it might be 50% more, but I'd just be cautious in assuming it will cost you less.