iZotope's Neutron 4 is a well-regarded mixing ... plugin with reduced functionality for a reduced price, typically around $50. For a limited time, though, you can grab Neutron 4 Elements for free ...

a Gate and a Mix knob. As a further bonus, the free download also includes a license for Silk Vocal Live, a realtime version of the plugin that’s designed for - you guessed it - live use.