I came across this post and thought id chime in, even though it is a couple years old.
There are two products I reccomend. They are ROCKTITE and QUIKCRETE hydraulic cement. The ROCKTITE is more liquid and fluid, great for pouring in cracks and holes on flat concrete. It stays liquid for about 10-15 minutes, then suddenly hardens up in a matter of a minute or two.
QUIKCRETE hydraulic cement is better for holes in walls and block, broken or missing corners and such. The hydraulic cement is thicker and can be applied with a scraper or putty knife.
Both are easily mixed with water in a bucket. Simply wipe area with a damp rag to smooth and remove excess.
Maybe one of these products will work for you, along with a sealer or paint. They are excellent for repairs and small jobs. I have not tried them on such a large area, but may be cost effective in some situations. I am curious to see what you decided to do. Best of luck!