This simple extension allows you to add a gift wrap option to your products with optional price.
WooCommerce > Settings lets you set up the default gift-wrappable status per-product and cost. These costs can be overridden per-product too.
If the customer adds gift wrap, it is shown in cart + orders, and adds your defined cost to the item cost too.
If you’d like to contribute to the plugin you can find it on GitHub: https://github.com/mikejolley/woocommerce-product-gift-wrap