Only millions? No problem at all.
Let's revise that estimate, though.
765,000 sworn state-level personnel in 2008. We'll round up to a million.
At $1000 each for hardened, certified cameras, that's a billion dollars. But we should expect them to last about three years, so $333M each year.
Storage costs are cheap, but secure handling of storage is not. Let's say one full-time $100K employee per hundred camera-wearing officers. That's a billion dollars per year.
So I'll go with a cost estimate of 1.3 - 1.5 billion per year for cameras for all police officers.
Is that worth it? I think so.