HELP! red roots and mahogony/purple ends

ok so this is the first time ive really boo booed my hair...this time around my start color was a medium to light brown with golden hilights that was the faded result of a permanet mix of a dark brown and a red color...though it had been a good couple of months since and had lightened almost 3 shades...anyhoo i stupidly used l'oreal's natural match in shade 4r (too bad my hair was lighter than i thought) end result i have bright red roots which kinda fade into a more mahogany/purpley hue...its really hard to describe but all i want is a dark brown with if possible a hint of auburn in it...i dyed it on thursday night and i know my window for fading is almost if not already gone...it has faded a bit but i think its going to end up with my ends almost back to the color i started with while the roots seem to be staying bright shiney red. please help! i really am not happy with the color and am really hoping for a cheap fix cause im a poor college student and the idea of having to pay tons to get this fixed is just torture!