MGM SC Guide 8, Fourth Edition: Pg. 130

The original correct sentence, according to the books is:
I will have HIGHER bills THAN last year.

If were to write a similar sentence say:
My sister is STRONGER THAN Brian.

This statement just means what is states.

However, if I tweak it a little and state:
My Sister is STRONGER THAN Brian's.

The entire meaning of the sentence changes. Now the comparison is between 'my sister' and 'Brian's sister'.

Now coming back to the original sentence, my doubt is if we are comparing 'bills from this year' to 'last year', instead of comparing 'bills from this year' to 'bills from last year'. I do understand that we can omit certain words, and in this case, the comparison is somewhat obvious, however just to follow the rules and keep the comparison logically and structurally parallel, shouldn't the sentence read:

I will have HIGHER bills THAN last year's. (Where the 's will point to last year's bills)
OR
I will have HIGHER bills THAN those of last year.

Thanks,
Divz

Your examples are actually preferred. Note that the book wasn't comparing its sentence to yours, but instead comparing its sentence to one that didn't even use the word "than"..

_________________
Tim Sanders
Manhattan GMAT Instructor