What do I do about my fading dye

Ive had purple highlights in my hair for the past few months now and its starting to fade. It first faded into a magenta then to a dull pink as expected. I originally got it done professionally, and I wanna re dye but it costs A LOT of money. So I was wondering what would happen if I took purple box dye and just went over my pre existing purple/magenta? I have dark hair so if I dyed my whole head, only the bleached parts that are purple should show (unless there's something I don't know, which is why I'm asking here)