• An idiom may be a group of words established by usage as having a meaning not deducible from those of the individual words. They're usually metaphorical and don't seem to be taken literally. As an example, the idiom ‘over the moon refers to extreme happiness.
• ‘The alpha and also the omega’ is an idiom that refers to the commencement and, therefore, the termination of something. It's not an awfully commonly used phrase.
• Now, we all know the meaning and usage of the given phrase. Let’s study our available options:
• Very costly items - This phrase refers to expensive objects. This is often not the precise meaning of the given phrase. It's not the specified answer. So, this is often an incorrect option.
• Assorted items - This phrase refers to ‘many items’. This is often not the precise meaning of the given phrase. It's not the specified answer. So, this can be an incorrect option.
• The beginning and, therefore, the end - This phrase refers to ‘the commencement and, therefore, the termination. This has the precise same meaning because of the given idiom. It's the desired answer. So, this is often the proper option.
• A nice act - This phrase refers to a good demeanour/acting’. This is often not the precise meaning of the given phrase. It's not the specified answer. So, this is often an incorrect option.

Hence, option C is the correct answer.