If you've never written a web application before do NOT start with something that involves billing. That's a good way to end up in a lot of trouble. Billing is hard to get right, and if you get it wrong you can end up facing huge fines or even in court. In most cases, you have to comply with PCI DSS security standards, and if you fail to do so and information is lost or stolen, you're likely looking at $500,000 in fines.
If you absolutely must do e-commerce, outsource it to PayPal or Google Checkout so that your risk is limited mainly to charging people the wrong amount by accident.
That warning out of the way, Rails is a good place to start if you've never done web development before. It has it's problems, but they'll go unnoticed until you've been working with it for at least two or three years. i.e., they're fairly minor, and are likely to annoy only a very experienced developer with significant project requirements.
Full disclosure: Google is my employer, so obviously I think you should opt for the Google Checkout option.