two crystals. These alone can cost more
than a whole clock.

Of the longwave radio frequencies used for time standards, 40kHz (JJY,
Japan), 77.5kHz (DCF, Germany) and 60 kHz (WWVB and MSF) crystals are
off-the-shelf items in the Digikey catalog at less than a dollar each.
I'm guessing their easy availability is because they are commonly used
in real receivers.

I've always noted with some curiosity that 77.503kHz, 60.002kHz, and
60.005kHz are off-the-shelf crystals too... used in a direct conversion
receiver for DCF/WWV to 3Hz, 2Hz, and 5Hz carrier-detect frequencies
maybe?

Tim.