An anonymous reader lets us know about a DIY synthetic aperture radar built for $240
in parts (give or take). Here's PDF slideware
from the Ph.D. student's research. "Using a discarded garage door opener, an old cordless drill, and a collection of surplus microwave parts, a high resolution X-band linear rail synthetic aperture radar (SAR) imaging system was developed for approximately $240 material cost. Entry into the field of radar cross section measurements or SAR algorithm development is often difficult due to the cost of high-end precision pulsed IF or other precision radar test instruments."