Since it still works, I wouldn't bother repairing it but it is a good idea to get a new one.
How did it crack - aren't the Macbook Pro bezels metal?
The machine itself is only worth about $300-400 used so a $225 repair would be a bit wasted.
You'll still get something for it second hand and Apple has a refurb section where you can get discounted models so that an upgrade isn't so expensive:
Last year's 13" is in there for $850 with mostly the same spec as the $999 11". They mainly just improved battery life this time round. Those deals are only available as long as they have refurb models so if you see a good one, it's best not to put off buying.
If you went for that 13" and sold your old one, worst case it should be a $450-550 upgrade and you get pretty much a new machine with a full warranty, which you can get 3 year Applecare on, which you can buy up to a year later.