Data cleanup will take twice as long, cost twice as much, and you will lose at least 10% of your data when you decide to finally give up scrubbing the data.
I actually independently came up with the 10% figure today as well, and mentioned to my project manager that unless he wants to invest real money chasing the long tail of data, he was going to have 10% of the records with bogus values in some fields. I will certainly adopt the rest of your quote!
I have since added a corollary: I do not do IT projects unless you pay me enough to retire on.
Here you lost me. Why were you even in this business if you didn't love the challenge? Don't take other peoples' bad data personally. Take it as an opportunity.