Careful with high concentrations of H2O2. A friend of mine works in textiles where they use 50%. A drop fell on the back of his ear. He did not know what it was that had hit him until it started burning. High concentration is a good oxidizing agent.
It might be cheaper to buy one bottle of 35% than 12 bottles of 3%. But unless you plan to use it soon it might not pay. The O2 tends to come out of solution once the seal is broken. Then concentration decreases.