salesforce plans page says that they charge per "user". Well, it makes sense to pay a few dollars per employee, but what about having non-employee users like customers of online banking? I have seen actual mentions of salesforce in ebanking. Where can I read about their pricing for that?
In this case, the banking users would probably be "portal users".
Setting Up Your Customer Portal
I think you'll have to talk to a sales rep about pricing, but it's typically a fraction of the cost of a full users license. There's also a similar license you should ask about called a high volume portal license.