E-Commerce "sandbox" for business ed

I teach Entrepreneurship at a college.  I'd like to have my students practice with one of the many online stores - cartfly is cool, amazon, yahoo, etsy.  All require a credit card or a merchant account.  My school works with PO's and such and the business office is not too flexible.  Have any of you found work-arounds or solutions to allow students to experience a real online 'lemonade stand"?