Costs associated with Merchant accounts

An internet merchant account will have three types of costs:

Up Front Application Fees
On Going Fixed Fee
Discount Rate
Fixed Transaction Fee
Termination Fees
Miscellaneous Fees

Up Front Application Fees
Many internet merchant accounts will require an up front application fee. This fee, supposedly, is to cover their costs for processing your application. In case you choose not to open an internet merchant account, they still cover their initial costs.

On Going Fixed Fee
Most all internet merchant providers require a monthly fixed fee or "statement fee" as it is commonly named, which is simply another way to cover their costs and make money. You will be hard pressed to find a provider that does not require this type of fee on a monthly basis.

Discount Rate
Usually, the discount rate will be between 2 and 4 percent. The discount rate is the sales commission the provider earns on each sale. For example, if the discount rate offered is 3%, and you receive a sale over your web site for $20, you will owe 60 cents to your internet merchant provider.

Fixed Transaction Fee
Usually between $0.20 and $0.30, the fixed transaction fee is the fixed fee portion of each sale. Unlike the discount rate, the fixed transaction fee is the same for every transaction.

Termination Fee
A termination fee can apply if you cancel your merchant account within a specified period of time (usually within one year). But some merchant providers require a three year commitment!

Miscellaneous Fees
If a customer requests a refund and they want their credit card credited, an internet merchant provider will charge you a separate fee (usually between $10 - $20).

Source - http://www.webmasterstop.com/13.html