Hey @Coelho63
Infinity theme costs $100 on Shopify at the moment, Feel free to check it out by Clicking Here. If you want to hire a Shopify developer who can design this theme and modify it as per your requirements then the charges differs from every Shopify developer. If you want me to help with your theme setup and giving it a right direction then feel free to connect with me and I would be more than happy to help with this. Good luck with your store!
Best Regards,
Moeed