I am not aware of such. The first step would be to pick a platform that can call webhooks and then do the integration. It sounds like all you’d need is to add the user (which might be done with sso) and then connect members with a particular group once they are registered.
Depending on how difficult the other platform is it work with and exactly what integrations you want, it’s likely in the $500 to $2000 range at a minimum, though it could be several times that depending on just what you want.