Using a simple ACF field you can adjust the WooCommerce pricing type per item with a dropdown selection that will display after the price in the product, shop, cart and checkout page. Create a select dropdown in ACF. This example…

You can change the WooCommerce price to be by weight by appending some text after the actual price such as ‘per kg’, this can be done by manipulating 3 filters that display the price in the shop/product page, cart and…