Shopify recently released its WordPress app - with a $9 a month Shopify account you can turn a WordPress site into your eCommerce site. Using the same Sync App as we recommend for Shopify you can sync inventory. For a total of $14 a month ($9 for Shopify and $5 for Sync App) you can be in business.

You can also use Buy Buttons to embed complete collections into any web page on the shopify lite plan.