Build a Sage 50 connector

We often develop cloud-based CRM systems that need to integrate with accounting systems. A small number of our customers would like the CRMs we build for them to connect to their Sage 50 (UK) installation. The (cloud-based) CRMs that we build would expose some endpoints and the Windows-based connector that you build would periodically call them to identify any new customers/invoices/payments/etc. and import them into Sage 50. Equally, the connector would periodically call Sage to identify any new customers/invoices/payments/etc. and call the CRM endpoint to export them. Becoming a Sage developer is expensive so I am exploring the possibility that another development company has the necessary licences in place with Sage to produce the connector, and can work with us to produce a connector that works for us, that we can use in any of our projects where a Sage 50 (UK) integration is needed.