I'm glad to see some folks on here involved with the JWST, thanks for all your efforts! I have a question: is the big cost primarily due to the one-off nature

I'm glad to see some folks on here involved with the JWST, thanks for all your efforts! I have a question: is the big cost primarily due to the one-off nature of the components, figuring things out for the first time etc? I ask because there's some proposals (ExoEarth Mapper) for constructing a giant array of 20+ of JWST-like telescopes in order to get pictures of earth-like planets. So if one JWST costs $8Billion, how much would 25 cost?