Have you asked for a day rate increase? If so, what did they say? If no...trust me....their not gonna just go ahead and raise it without you bringing the issue up.
If you DO ask for a rate increase, a jump from 300 to 500/day most likely isn't gonna happen. Not to say that you can't earn that rate elsewhere. The suggestion by Nick for a yearly increase is a good one.
It sounds like you are confident in your job skills, but it also sounds like this is the only post facility you have ever worked at (that's my assumption based on your post...I could be wrong). You may find that you need to start freelancing at other facilities in order to move up the day rate ladder. But remember...most places hire editors to edit and producers to produce. The places that hire "preditors" don't necessarily pay more because of the extra skills, they are just trying to get more bang for their buck.
Bryan Keith
http://www.happylandstudio.com
