I've got a site that would like to start selling the calendar that it promotes. The calendars are relitivley inexpensive ($20) and the site revenue is not that high.

Is it best to:
A) Get a merchant account and do things that way
B) Use a payment gateway
C) Use good 'ol paypal because there is an API already built

There is the possibility that this site could partner with an existing (traditional) store that already accepts credit cards. Does this matter?

Any help is greatly appreciated.