You can also get a range of child themes for Storefront in case you want to customize the look of your store further. Most of the child themes are available at $39 a piece (occasionally, though, there are themes with price tags as high as $119). If you're a developer with ecommerce clients, they have a package for $399 where you get all of the themes in the library.
What it all comes down to is that although WooCommerce is technically the cheaper solution, it will require much more work to set it up, and you'll need to be more careful not to go over your budget, as every additional extension comes with a price tag. In the end, with WooCommerce, you're spending more time on setup and management, which translates to dollars.
Imagine an ecommerce platform that allows customer service reps to have a single view of a customer across all channels, a centralized order and inventory management system that can efficiently fulfill orders from all your sales channels, including brick and mortar stores, or utilize a customer's order history data to provide personalized and relevant offers. The possibilities brought to light with the advent of a complete ecommerce platform for business optimization and improved efficiencies as well as deepened customer engagement and satisfaction are limited only by one's creativity.
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.