If you're interested in setting up an e-commerce site, you should seriously consider using Google Checkout. I recently set up my account and it's been very useful.
Step2
While setting the account up is free, you will pay just 2%+20 cents per transactions, but that's normal for a merchant account. But, you only pay when you sell something, no monthly fees!
Step3
Having this account allows you to set up an entire e-commerce website, or simply use "Buy It Now" buttons.
Step4
To get started, visit //checkout.google.com/seller (link provided below, under the resources heading). This will give you all of the details and the application to set up your account.