This all depends on the payment methods you choose. In most cases there's a standard fee that is a sum of transaction fee and commission fee. The transaction fee is a fixed value, and commission fee is a percent value (it varies depending on the transaction amount).
Most of our payment services (like recurring billing or single-click payments) are free of charge, although several (e.g. 3-D Secure) may require additional fees. We also don't charge any set up fees, although in many cases there may be a monthly fee.
It's always best if you contact us directly, so we can provide you with more specific insight that pertains to your case.