My suggestion would be to replace it yourself if you have the ability/time. I did not but I would also suggest you replace it with an after market manifold or most likely you will be doing this again in the next few years. I have heard the stock manifolds and OEM replacements are just poor quality.
I went ahead and replaced mine, also cracked, with a Banks Revolver and that thing is a hoss and something I shouldn't have to worry about for a long while, at least I sure hope because it wasn't cheap. That labor quote seems good as I have been quoted $332 by more than one shop, this is 4 hours according to the book and one shop said 6 hours.