The price is $1.00 per megabyte of email processed. This charge is asessed when a) when you paste email into SpamCop's reporting form and hit "parse" or b), when you click on the link to go to the parsing page for spam submitted through the SpamCop's email submission system.
Also, if you break the rules, you may be charged a fine. For more details, see the rules FAQ.
When you subscribe, we bill you for however many bytes you choose to use, and we warn you on the homepage when you run out of "fuel." It is always your choice to add more bytes, and we will never send you email telling you your account is dead. If your account remains unattended and unpaid for a long time, it may be terminated.