I've gotten SPAM telling me the reats for sending SPAM (a company trying to get more SPAM sending business). It was something like $250 for one illion e-mails. I'm guessing that the cover the $150. THey only need a few responses out of millions.
I also went to the web site of a SPAM advertisement (for anti-virus software) and started poking around. I found the directory with a list of their buyers. It was relatively long. About 200. So, yes, SPAMers make money. I refuse to buy anything from a SPAM ad. It's a shame a few in a million buy.
You'll probably be interested to know that the cost of sending out one million emails, at retail transit prices, is less than a buck. Yep, you heard that correctly: sending a million emails costs under a dollar.
The spammers usually work in cartels of a half-dozen to a dozen spammers with their own specialties, In my experience, the average cartel is generating an honest gigabit/s of email at any one time, multi-homed across multiple backbone providers. To put it another way, one of these cartels is constantly sending enough email to saturate 1,000 T-1 circuits (my math isn't bad, you lose about a third of your effective bandwidth on T-1 circuits due to protocol overhead).
I think people underestimate the scope of these spammer cartels. These guys have bandwidth that is on par with the biggest corporate Internet sites. And they don't make chump change either. A cartel can pull in a couple million a year (net!), split among a several guys. And that is why spam is bad and only gets worse, and the cost of doing business is getting cheaper with time as well.