Nazario has seen DDoS attacks offered in the range, but according to SecureWorks Security Researcher Kevin Stevens, prices have dropped to $30 to $50 on some Russian forums.

And DDoS attacks aren't the only thing getting cheaper. Stevens says the cost of stolen credit card numbers and other kinds of identity information has dropped too. "Prices are dropping on almost everything," he said.

While $100 per day might cover a garden-variety 100MB/second to 400MB/second attack, it might also procure something much weaker, depending on the seller. "There's a lot of crap out there where you don't really know what you're getting," said Zulfikar Ramzan, a technical director with Symantec Security Response. "Even though we are seeing some lower prices, it doesn't mean that you're going to get the same quality of goods."

In general, prices for access to botnet computers have dropped dramatically since 2007, he said. But with the influx of generic and often untrustworthy services, players at the high end can now charge more, Ramzan said.