For a while there was a program where they would replace cracked top cases (the part with the keyboard) within 2 or 3 years of purchase. Some people who went in for that repair got lucky and Apple replaced other parts (I think a few people got screen bezels replaced for free).
I don't know if (1) the program is still going on or (2) if they would also replace the bottom case.
No harm going to the Genius Bar and seeing what they can do.
Good Luck!!!