231450 E-Commerce - Digital Downloads

My client wants to sell digital products on her website - MP3 files she is recording. We would like to use PayPal to accept payments. Google Checkout would also be acceptable. The site is already built - you can see it at http://quantum-therapeutics.com. We want to use osCommerce, unless you have a better suggestion for the shopping cart. We need you to install the shopping cart, skin it so it matches the rest of the site perfectly and seamlessly, and hook up the payment gateway. Please give me a cost and time line for the project, as well as any e-commerce recommendations you have. Thanks.