I'm Ann, from the team here at Shopify :)
Not sure if you've seen this yet, but we actually have a list of third party experts here! These are developers, marketers, designers, etc, who we have vetted, so we know they know their way around Shopify. You can scroll through the list of App Developers and reach out to a few to see if they would be willing to collaborate with you on this project and what they would quote you for it.
Additionally, that page also has a Job Board, where you can post your idea, and have developers reach out to you about it! Check it out here.
I hope this helps! If you have any more questions or concerns feel free to reach out to us on this thread :)
Have a great one,