1 Depending on the week, the cost for the ideal protein diet after the initial amount paid is going to range anywhere from $30 to $90 per week. 2  The longer you stick to the program, the less you are going to have to pay per week. The longer you stick to the program, the less you are going to have to pay per week. 2  According to 3fatchicks.com, it would cost you an average of $84 per week to invest in this kind of diet, which means that the Ideal Protein Diet plan cost is around $3 to $4 per meal that is $12 per day.