You can code this directly into your theme, without using a store facing app that could potentially slow your load speed.
1. Set a banner to show either in the header or on the product page, saying something like "Free shipping at $50" or "Add $24.65 to your cart to qualify for FREE shipping".
3. You would retrieve the cart contents after each action on the cart (adding / subtracting product).
The implementation would depend how your theme is set up, but a Shopify developer will be able to investigate and provide a solution.
If you can find a low priced app to do it, that might be worth it while you're testing the feature. Something like this though I would recommend coding directly into the theme eventually.
If you don't have a go-to developer and need help finding one feel free to contact my team at orderautomator.com/support. We make Shopify apps, but have a network of Shopify experts we work with, and can recommend you a developer if you need one.
To display a free shipping threshold and encourage customers to add more items to their carts to qualify for free shipping, you can use the BoldieAI - Upsell & Marketing app. This app offers several features that you'll find beneficial:
Progressive Messages: If you have a minimum order value for free shipping, this app's free shipping goal countdown can be incredibly helpful. It keeps customers informed about how much more they need to spend to reach the free shipping threshold as they add items to their carts.
Ready-to-Use Templates: You can get started quickly with pre-designed templates for the Free Shipping Bar, saving you time on customization.
Geotargeting: Tailor your message to visitors from different countries by setting up separate bars based on their IP addresses.
Auto Currency Converter: The app automatically displays prices in your visitors' local currency based on their location, providing a seamless shopping experience.
By using these features, you can enhance your store's ability to offer free shipping incentives and potentially increase your sales.
If you have any more questions or need further assistance, please feel free to ask.