For now, I'm building TicTacSyncs with off the shelf boards, here an Adafruit Ultimate GPS FeatherWing (25 USD) and a Adafruit Feather M0 Basic Proto (20 USD):

Flash the board using the Arduino IDE with this program: ppssyncYears.ino

A motivated maker could lower the GPS cost using a custom breakout board and a raw  Raw L80 Quectel module. Total project cost: 26 USD + USB power bank.

How's that for a subframe (80 μs) zero-drift/no-need-to-jam-sync  solution?