For design to Shopify projects, the most accurate quotes come if I’m able to see the actual design I’d be building. If that is not possible, wireframes and/or an overview of the functionality included in the site and different page templates that would be involved will allow me to at least roughly ballpark costs for you. I won’t commit to a final number without seeing the final design files, however. If you need custom email templates developed for Shopify notifications, including that information is most helpful, as well.