Based on my current design iteration for the RF board, the bill of materials consists of 1x HMC431LP4E VCO, 1x HMC717LP3E LNA, 1x HMC219AMS8E mixer, 3x HMC476MP86E gain blocks and 3x SMA connectors (Molex 0732511150). At single-unit quantities from Digi-Key, those will cost you about USD $60 in total. I have excluded a few parts, such as the passive capacitors and resistors, but they're quite inexpensive and this is just a very quick budget estimate. Obviously the IF signal processing components are all excluded too, but the RF parts account for the majority of the cost.

When we consider that something like the Mini-Circuits ZX05-43MH-S+ mixer specified in Greg Charvat's 2011 MIT IAP radar project (a major source of inspiration for this project) will cost over $40 alone (and the VCO, each gain block, and the LNA each cost approximately that much again) it is clear that my objective of a substantial cost reduction (compared to Charvat's design for his students' projects as the "reference design") has been achieved.