Brand Undisclosed

Check the listing for details. Adafruit DS3231 Precision RTC Breakout. Condition: New. Listed at 17.50 USD. And, hey, it does exactly what it says on the tin! This is the finest RTC you can get, and now we have it in a compact, breadboard-friendly breakout. And that's all well and good, but those crystals have slight drift, particularly when the temperature changes (the temperature changes the oscillation frequency very very very slightly but it does add up!).

$12.25
$17.50