Quantify the amount spent on the mass of the telescope --- in other words, the actual materials.
Quantify the amount spent on the functionality of the Hubble Space Telescope. This includes the budget towards providing power for the telescope's instruments, spacecraft and data transmission.
Determine the complexity of the telescope architecture. Based on the complexity, estimate the time and money costs of developing the technology and component specifications necessary.
Compare the costs to the benefits. Benefits may be intrinsic (an increased understanding of nature), economic (increased jobs in the aerospace industry) or technological (spinoffs in unrelated industries that either benefit the economy or increase quality of life). For the Hubble Space Telescope, the primary spinoff so far has been CCD chips for digital imaging of breast biopsies. CCD chips image breast tissue more clearly and efficiently than other technologies, enabling doctors to detect the difference between malignant and benign breast tissue without doing a surgical biopsy. CCD chips reduce medical costs by thousands, and have saved hundreds of thousands of women substantial time, money and pain.