lake How do you remove semi-permanent hair dye? How do you dye over semi-perm. hair dye?

I have my hair red (http://farm4.static.flickr.com/3079/3111141022_b35a3aa2c7.jpg?v=1229366257 , http://farm4.static.flickr.com/3195/3284559572_6650a5a264.jpg?v=0), but it's fading and I want to go back to my natural hair color; dark brown. I've tried this before, but it turned a deep brownish burgundy/purple and back to a light purplish gray. So.. I redid the red. But my hair is growing fast and the red dye is too expensive (13 a bottle) to keep up with this hair color. One bottle isn't gonna cut it anymore.. How do I get this crap out so that I can dye my hair back to dark brown, and keep it brown?there