have you considered finding a less-expensive, color-treated shampoo? there are shampoos there are are definitely cheaper than what you are using now, but in the 10-15 range that are going to protect your color with (imo) better quality ingredients than drugstore brands.
Brilliant Brunette...I've used both the voluminzing and moisturizing ones with pretty good results. Considering I spend a grand total of 0 minutes styling my hair in the morning, my hair falls pretty well, smells nice, stays clean, and gets bonus points for bringing out the brown tones in what would be my otherwise jet-black hair.
I've also used Fructis and enjoyed that experience as well.