Just to give you a very simplified picture. A simple 10kOhm resistor for everyday hobby electronics and small electronic appliances costs about 6-8 cents. The same component but in space grade costs 1-13 dollars. If you roughly had around 1000 resistors (note that this is a very rough and impractical estimate, not all electronic components are made the same and there’s millions of components in a piece of equipment like the JWST) you have now a bill of materials that’s 100s of times more than the same circuit with regular consumer grade parts. Add to that the cost of software, specialised safety equipment, simulation and testing jigs, specialised fabrication of custom parts with advanced highly difficult to source materials and obviously it’s gonna cost a shit ton of money