If you were able to launch and rendezvous in orbit, I wonder how much cheaper something like the JWST gets if it could be built up piecemeal? The unfurling mech

If you were able to launch and rendezvous in orbit, I wonder how much cheaper something like the JWST gets if it could be built up piecemeal? The unfurling mechanism itself exists because of payload width limits. How much cost is bound up in "we can't just keep launching rockets because rockets are expensive" and how much is bound up in "precision technology for precision observations"?