Do it like a local! You just need to have a look in the "mamasound" website or you can also find the magazine in all the good places in Montpellier. 

Inside, you will find all the events who will happen in town, the places and of course the prices. There are so many things to do for free in this city. 

Since few years now, mamasound organize himself some events and trust me, it is always great!