I need to understand if I could say "As good a [noun] as it gets". Would it mean "the best [noun]"? E.g.
You can buy as good a car as it gets in that store.
I agree with Edwin; it doesn't work to insert the noun there.
I would, however, accept the noun placed within the phrase a bit differently, thus:
In this case, you are simply substituting the noun ("a car") for "it," rather than adding "a car" to the basic structure of the idiom. And yes, if you make this substitution, you would be saying it is "the best car."
You could not, however, use this version of the idiom within the type of syntax found in your example sentence. (That is, it would not be grammatical to say, "You can buy as good as a car gets in that store.")