US payment gateway

Cost effective is payment processors like 2checkout.com, clickbank etc.

But try Authorizenet if you really want your own payment gateway. But this costs you much in this early stage of income. Because you need your own merchant account and pay every month for payment processing etc.

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Paypal has a payment gateway + merchant account where you can accept cc on your site.

Guests can use their credit card without signing up for PayPal if you use PayPal Express also. The thing is they are removed from your site while paying with this method.

If going for a merchant account be aware of the PCI Security Compliances followed by most of the major credit card companies.
https://www.pcisecuritystandards.org/index.shtml
If you get chosen to be audited and fail there are some hefty fines to pay.
Be sure to read all of the fine print on any merchant agreement before accepting it.

PS: Be sure to read up on chargebacks and and understand what "reserves" are.
Reserves are when they will take or hold an amount of your money (often several hundred dollars or more) for this reserve, often without telling you. This is used in case you cannot cover the cost of a chargeback.

A chargeback is when someone disputes their cc transaction and you have to refund them. Most often when a claim is filed the merchant seldom wins. There is also a fee attached to this. Most often it is $25-$35.

thanks for the replies.. i did check on paypal and they got a .30 + 2.9 % transaction per sale which is fine. but i heard they also have a 30$ monthly charge, is that true.