What you need to do honestly, is "cheat the trade". You need to call a few companies for "estimates", and each time they come ask that question, "Does the WHOLE thing gotta get replaced?" If you get plenty of yes's, then do it. If not, I would simply flash patch it with either hydraulic cement or see 10-60 or 10-61 Rapid mortar. The rapid mortar would be best b/c it allows you to do entire horizontal surfaces, and is used for strength gain.
http://www.buildingsystems.basf.com/productdetailPage.asp?prodID=1
http://www.buildingsystems.basf.com/productdetailPage.asp?prodID=1