I saw this in Wikipedia:

"The JWST has a history of major cost overruns. In 2011, the United States House of Representatives voted to terminate funding, after about $3 billion had been spent and 75 percent of its hardware was in production. Funding was restored in compromise legislation with the US Senate, and spending on the program was capped at $8 billion. As of December 2014, the telescope remained on schedule and within budget, but at risk of delays."

Source: https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

Some things ARE expensive because they are difficult, require quality components or processing. I would rather spend on difficult science than on dumb bombs...