> I wonder how much cheaper are land-based telescopes over the lifetime of instruments such as the Hubble or the Webb.

10-100 times cheaper. An LBT night is around $50k-100k, which over 10 years corresponds to $300 millions. JWST total budget is about $10 billions.

True, JWST can operate close to 24/7. On the other hand, land-based telescopes are under constant refurbishment and upgrades, and they become more powerful over time.