Well ingoring the fact that I have been working on killing spam which means
I could attribute much of the cost of emplying me to spam I see the
following costs of spam:
1) It takes a lot longer to identify the wanted messages on my RIM pager.
2) A lot of uses of my mail system are slow because I am wading through
spam.
3) Most of the spam is simply never read, but some is because it takes a
while to check.
4) I frequently loose wanted messages amongst the noise.
I don't think that these add up to $1 per spam but it is a non-negligible
amount.
The total enterprise costs are somewhat different, here we have to take
account of the pinhead factor:
1) People who open up malicious code
2) People who defraud the company hoping to pay it back from a 419 scheme
(several really large frauds)
3) People who sue their employer claiming that pornospam created a hostile
work environment
For ISPs the major costs are:
1) Customers switching to another ISP to avoid their spam
2) Customers discontinuing service altogether
3) Complaints from customers, spam victims other ISPs and anti-spam
vigilantes with attitude
I don't think the cost of actually moving the stuff arround are the biggest
cost for anyone, they can become a major cost for a really big ISP which has
football fields worth of equipment.