If you want to start an e-commerce site without sacrificing too much on the cost, MarketPress has available themes and plugins to help with e-commerce startups. MarketPress offers a lot of free themes and plugins available for WordPress users.
FlexMarket is a free MarketPRess theme that is fully responsive and is built using the Twitter BootStrap framework. It has powerful options panel with drag and drop page builder. MarketPress contains more than 500 Google fonts, has unlimited customization options, ability to load custom logo, background images, and patterns, and so much more. Did I mention that this theme is free?
And to help with your start up here is a floating cart plugin available for free. This is an extension offered by MarketPress themes which lets you create a shopping cart that hovers or floats above your website. When clicked on the tad, it will launch a modal window which will display the customer’s shopping cart items and subtotal. Subtotal updates almost immediately just like in Amazon.com.
So are there things still hindering you from creating you own store? You probably need to read the full details: http://wpmu.org/free-marketpress-theme-and-floating-shopping-cart-extension/