A few years years ago we built a service on top of Sage CRM to do this for an end-user who sends to over 100,000 MailChimp subscribers every Friday . The MailChimp API is well documented and pretty straight forward. We also mapped to the the MailChiimp interests endpoint (Group Names) which allows the subscriber to choose to allow Bulletins etc. rather than a blanket Opt-out of all mailing.
Once you have the connector in place, you can also bring back into CRM some nice data such as https://bit.ly/mailchimp-sagecrm

A few years years ago we built a service on top of Sage CRM to do this for an end-user who sends to over 100,000 MailChimp subscribers every Friday . The MailChimp API is well documented and pretty straight forward. We also mapped to the the MailChiimp interests endpoint (Group Names) which allows the subscriber to choose to allow Bulletins etc. rather than a blanket Opt-out of all mailing.
Once you have the connector in place, you can also bring back into CRM some nice data such as https://bit.ly/mailchimp-sagecrm

What would something like that be per month in terms of cost associated?

Hi Jacob04, not sure if you're a partner or end-user. We work with half a dozen UK partners and 2 in the US, not direct.  Most of our simple extensions... things like CRM address map geocoder etc. and this are free. 

Hi, we are US based and I am an end user. What partners do you work with?

Ping me a message on LinkedIn Jacob04 and we can take this offline, not all Partners are comfortable for end-users to know they subcontract their CRM projects out.

I don't use linkedin can I DM you here?

Sure Jacob04 of course, unless you just want to ask your business partner and they can reach out to us. Even if we don't currently work with them, we should be able to help out.