You spent how much money on a perm - and now are willing to wash it away with $6 shampoo??
Dont do it - spend a little more.... even salons like BoRics and Hair Cuttery sell "real" shampoo's and generally on special, too.
You can get a liter of shampoo and conditioner - for chemically treated hair - for under $20. Liters last forever!!!
I highly, highly reccomend spending some money for shampoo on chemically treated hair.