I have not bought shredded cheese in probably 10 years. Reasons being, 1. shredded in a bag is coated so it does not stick together, this also hinders the melting ability as well. 2. shredded in a bag is more costly because it is another step, plus the coating, is another step, both add to the cost.
I buy all my cheese in block form, real cheese from New Zealand, Europe, and some from Thailand. Shred it yourself to save the money and you have a good base for cheese sauces and such that will melt evenly and smoothly.
It is between 80 and 100 grams of block cheese to 1 cup of shredded.