some hosting companies let you use their shared ssl cert, so when the user goes to checkout it switches to your hosting providers url but its still your site.
authorize.net has a simple method that lets your customers checkout on their site, then whenever you are making good money you can upgrade to the advanced method of integrating the payment on your site. they are my favorite so far cause its very easy to code with some knowledge of php with curl and they even give you some sample code.