OpenCart Setup Fee Extension Development

I need an extension for my OpenCart 2.2 store that allows me to add a one-time setup fee to any product without it multiplying when customers increase the quantity.

Key Requirements:
- Apply setup fee only once per product, regardless of quantity.
- Setup fee should be selectable for each product individually.
- Ability to set different fees for different products.

Ideal Skills & Experience:
- Strong expertise in OpenCart, especially version 2.2.
- Experience in developing custom extensions.
- Familiarity with product pricing and options in OpenCart.

Please review the existing extension for reference: https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=14755&filter_search=Setup%20Fee