Radar is cheap now, thanks to semiconductors getting smaller and faster the analog front-end which used to be a long expensive chain of components is now much smaller, the ADC is now faster, more accurate, and cheaper, the processor is now fast enough to keep up with a higher bandwidth signal. You could probably drive a very rough radar system directly off a Pico's GPIO and ADC, maybe toss in a decently fast op-amp for a receive amplifier.

Where you will run into issues is processing radar signals into usable data. If you're happy with the results that radar was giving 30 years ago then it's fine and dandy, but the magic of modern radar is in the software, not the hardware.