Discussion Forum—A Way with Words, a fun radio show and podcast about language

Yeah, it came from the dumbing down of American English.

And it will continue to count as dumb until it has become universal, from which point on only intelligent people will be capable of learning that it is correct. The dumb bunnies will then begin to say "those are a saving of $24" (after all, it's two or more dollars ain't they?). And after a time that will have become universal and therefore correct, and will thereby have moved beyond the intellectual reach of its dumb originators, and intelligence will once again be required to learn that it is indeed correct, and the dumbbells will begin to say, with a completely straight face, the grammatically abominable "that's a saving of $24".

Language rules are observation, not arbitration. The language got there before the rules were formulated.

"Savings" is a singular noun. There is no such thing as a "saving".

Without comment on eli_damon's claim, in your example, saving is a gerund formed from the verb to save and not a true noun. It is like:
Playing basketball is fun.
Reading is an important skill.
Her joining the military was a bold move.

I have found several dictionaries that include uses of both saving and savings as nouns, listing savings as taking a singular verb, and showing examples of a savings.