$50 to $60/hr. is pretty standard (at least at NYC networks and post houses). It never hurts to ask for $60/hr right off the bat. Most places have set rates that they’ll pay their freelancers, so if they tell you that they’ll only pay $50, take it. Don’t argue about it, or you might not get the gig.
Also make sure to ask plenty of questions before you take the gig, especially with regard to graphics and effects. For example, will the graphics be provided for you, or will you have to create them from scratch? What effects plug-ins will be available to you? It would be a looong session if you got there and found out that their Avid is equipped with Boris, and you only know Sapphire (or vice-versa).
Good luck!