Installing WooCommerce is free, but integrating the shopping cart completely with the system requires additional investment. Moreover, if you don't know WordPress, you won't know how to use WooCommerce. But the biggest problem with WooCommerce is its lack of scalability; as your business grows and you get more sellers, products and customers on your database, WooCommerce starts slowing down.
BigCommerce is most easily compared to Shopify. Both platforms offer a similar experience when building an ecommerce platform. Like Shopify, BigCommerce offers a range of prices and packages tailored to different types of businesses. The platform is highly customizable if you are comfortable with some light coding. It is also possible to use themes and templates to build your website, but some of these will come at an additional cost.