New stadium costs around to 400M rebuild about 150M
Say a new stadium is ready for 2014 if it was being built now.
Say Rebuilt Anfield is finished in 2017 (if it happens at all).
Two years of lost income while it was being rebuilt, plus the extra 3 years of being stuck without the extra income = you're talking more than £100m. The rest of the difference between a new build and a rebuild could be done with naming rights.
You can work the figures both ways, but we don't know if the owners are even going to commit to a rebuilt, or if they'll be here long enough to see it through.