Put role-based access control (RBAC) approach outside the API Gateway layer

We were very excited to use Kong Enterprise, because we need to implement an architecture based in microservices. However, the price is so high to us and the only enterprise functionality that we need is RBAC.

So our question here is, is there some approach to use some RBAC service, outside of the API Gateway layer, but giving all the set of roles and permissions to the other services?

Thank you!