Ha. The James Webb telescope is implementing a ton of new technologies and manufacturing techniques. Building a second one would presumably cost significantly less than the first, although I have no real basis for making that claim.
The Hubble Space Telescope (HST) is basically a civilian version of the KH. And the National Reconnaissance Office (NRO) is launching one of those KH satellites every couple years. I bet the latest one (USA-290) has much better tech than Hubble and would make a good replacement for Hubble, with few modifications required.
JWST is fundementally a different type of space telescope from Hubble, all of which contribute to its costing:
* It's being deployed at L2 Lagrange point instead of LEO - so the launch costs are even higher.
* HST had the insurance of knowing that repair was possible - JWST does not (both due to it's ___location and lack of capability) and so everything drags on even more to try to reduce risk
* JWST is technically more complicated. The thermal management system needed, and entire origami unfolding mechanism alone would make it more complicated and expensive. This doesn't even start looking at the optics.
