Set up shopping cart in blog, product download, Ravelry.com

I’m setting up a self-hosted blog for a fiber artist. She would like to sell patterns from her site and allow users immediate access to downloading the pattern. What’s the best way to do this?

She hasn’t decided on whether to use credit card capabilities or simply Paypal. Pros/cons, other than cost? Does WP provide credit card plugins?

I’ve found a blog that upon the user’s purchase click, completes the transaction through Ravelry.com. Anyone familiar with this?