$2500 per million may keep some spammers away, but I believe you are correct -- They are selling access to unfiltered in-boxes. As I have said many time before, follow the money. Spamming and virus, which includes detection for both is big money. Lots of big money from the anti-spyware, anti-spam, and anti-virus, companies going into pockets. Too much money to be made for out pols to take action.
I don't see cost as much of a "deterrant" to spam.
The market is smart enough to pick the price at which both spammers and providers make money.
If they won't pay 2 million for 30 seconds on the Super Bowl, maybe they'll pay 1 million.
All that's lacking is the negotiation.