API Interface to Shipstation API and also for updating via csv or xcel files from FTP location

I am looking for someone to set up an API interface between an ecommerce website that has a Rest API available and to shipstation. This part of the project will pull order details from website to shipstation and after product ships send tracking info back to website and show item is shipped. Also, want an interface to pull data from xcel or csv files located at an FTP location in order to create listings, modify listings, make changes to listings, end listings, etc. I will give more details as needed. For now I would like to know the ballpark cost for setting this up. Thanks.