Yes there are plenty! You can check out Vajro. If you own a shop in shopify or Woo Commerce you should be able to get your own app. http://vajro.com/
You can have options to build mobile app for eCommerce store other than Shopify and WooCommerce. Some of the best known eCommerce platforms are Magento, PrestaShop, BigCommerce, 3dCart, CoreCommerce and many more.
You can find a team of developers who will do this application for you. The task is not complicated, so it will not be very expensive. Smth like $1000. The best option is to look for a team located in Europe, because their per hour rate will be lower. A mobile application is a great idea, because more and more people prefer purchasing using their cell phones/tablets, etc.
You can try open cart for your ecommerce site as it will provide both responsive and desktop based outlook. But especially for mobile app, you can take help from an android developer or you can create your own. For example check my app, its an app for my ecommerce site.
Magento is one the best ecommerce platforms which now allow you to develop mobile apps as well. However, because of the popularity of Magento, many tools are developed that allow you to easily convert ecommerce store to M-commerce. You can explore them if you already have a desktop application.
Very easy to execute even for a web developer. Please shop around for 5 strong potential candidates, ask for previous examples that are as close to what you want to achieve then make sure they will get along with you and deliver successfully before starting the work. Break the project and budget down into milestones so that you dont get burnt and to continue to motivate the freelancer, consistently through regular payments which should be made on time
You can develop mobile apps easily using phonegap build and woocommerce I have my app named Swapthebook in google play store i can help you in creating such app if you want