Sure, there's a ton we don't know yet about Jupiter and Saturn...but for reference Juno cost 0.1x the amount of the JWT and observed Jupiter from one million times closer [0]. Is the JWT really the most economical way to make these observations?

[0] https://en.m.wikipedia.org/wiki/Juno_(spacecraft)

In general, these types of flagship facilities (JWST, Hubble, etc.) are funded by the government (via NASA in the US). In some cases, larger ground-based observatories (e.g., Keck, Large Binocular Telescope) are funded by a combination of private consortia (consisting of foundations and public/private universities) and competitively awarded scientific grants (e.g., from the National Science Foundation, in the US).

The operations are generally paid for by the above sources. Researchers apply for time through a competitive proposal process where ideas for using the facility are collected and evaluated, with proposals awarded telescope time based on scientific merit and technical feasibility. Sometimes, particularly for investigators located in the US working with space telescope data, funding is awarded to the investigating team along with the telescope time. This funding is used to support the analysis of the collected data (e.g., to hire faculty/postdoctoral researchers/students, purchase computers, etc.). For ground-based facilities, researchers often apply for funding from the National Science Foundation to support the analysis of their data.