I need to get rid of my blonde peek a boos

[changeisgood]

I have naturally dark hair, and dye it a few shades darker with a few blonde peek a boos. I am a single mother of two so on a tight budget and am looking into using store bought dye to dye my hair all one deep brown color. I am unsure if there is a special process to do this in regards to the blonde, can I just use one step color? Will it actually take out all of my blonde and make it the same color as the rest of my hair? HELP!!