1. A computer-implemented method for tracking costs associated with virtual control planes, comprising: under control of one or more computer systems configured with executable instructions, establishing a virtual control plane of a virtual resource provider in addition to at least one other control plane, the virtual control plane implemented at least in part by a first set of control plane modules that includes at least one custom control plane module configured at least to replace functionality of at least one of a set of default control plane modules; receiving a first set of resource configuration requests from the virtual control plane over a period of time, the first set of resource configuration requests specifying at least one configuration for a set of virtual resources maintained with a set of implementation resources, the at least one custom control plane module performing management activities over the set of virtual resources; mediating the first set of resource configuration requests with respect to a second set of resource configuration requests received from said at least one other control plane, the first and second sets of resource configuration requests at times competing with respect to the set of implementation resources; determining at least one cost to operate said at least one custom control plane module during the period of time based at least in part on at least a mediated subset of the first set of resource configuration requests generated by said at least one custom control plane module, the at least one cost to operate said at least one custom control plane module being distinct from costs associated with the set of virtual resources; and providing to a user a presentation of at least one cost to maintain the virtual control plane during the period of time based at least in part on said at least one cost to operate said at least one custom control plane during the period of time.