Costs & Time
If you order the Standard Parts according to the sources indicated there, you have to calculate with about 195 Euros including sales tax and shipping costs.
Special & Small Parts
If you order the Special- & Small Parts as a kit from me, 100 Euros including shipping costs will be added. Value added tax does not apply for you, because I am registered as a small entrepreneur (Kleinunternehmer) according to (German) §19 Abs. 1 UStG.
The total cost of the alarm clock parts is about 295 Euros.
Depending on your experience and tooling, you have to expect about 30 to 50 hours as working time. Including the time for shopping research, ordering, preparation and soldering of display and control elements, working of housing and lower front panel, assembly of board, assembly of all parts, software installation, adaptation of constants, functional tests and wall mounting.