Hello,
let me offer you my prestashop skills. I can extend your prestashop so default product position in category and search results will be managed by your extra field.
I can finish this as standalone module in 3 days.
===============
I work daily with prestashop over 5 years. I know prestashop from top to bottom. I am familiar with every aspect of this eshop system. Prestashop settings, tweaking, modifiing core and theme files, custom module development, you name it.
You can also check many of my positive reviews here on freelancer.
Thank you for your time.
Best Regards,
Jarda Nalezny