it depends upon components used
lcd based clock or seven segment based clock ,led matrix clock
mcu based non mcu based
first of all you have to select what type
There is no simple answer to the question as posed. The device you show as an example probably cost tens of thousands of dollars to prototype. The molds to make the plastic parts cost more tens of thousands. In mass production (10 million units or more), the cost is less than $2 but to make just one might cost $50,000 or more.
Please don't cross post or repost under a new heading.