Hi, I have recently worked on similar project like this. Integrated TCS API with Shopify Store. I can do this job easily for you with lowest cost and high quality. Things required are a server with SSL certificates installed and API details with documentation.
With about 7 years experience in web development and 5 years experience in shopify, you can be assured of a quality result from my side, please let me know if you have any query for me, and I would be glad to answer.
Looking forward to working with you on your job.
Thank you.