We have a billing system you can use.
Place your PayPal email address between the billing tags, and the price in centwise value as the attribute.
Example:
[bill=100]HeraldsPayPal@gmail.com[/bill]
^^ If you private message someone that code, then it will send them a bill for $1
When they Pay the bill, PayPal will send you an email with their mafia account name, telling you that they paid.