Hello,
My name is Valerie. I'm a part of BelVG team. Our team is an official Magento Bronze partner, we have 12 Magento certified developers and Platinum Prestashop Web Agency with 8 certified Prestashop developers. We had a lot of experience in API integrations with various platforms. In our portfolio you can find search options integration, BlueSnap payment gateway integration with Magento and Prestashop, 2Checkout payment gateway integration, marketing tools integration, ZendDesk integration etc.
To make an estimation on you project we need to have a look at your API and documentation if you have any. We also need a list of minimum required functional for the first version.
Thanks and look forward to hearing from you.
Best regards,
Valerie