Some teachers have formed groups to buy supplies in bulk from retailers like The Dollar Tree Inc DLTR.O and Walmart Inc WMT.N. By Gigi Zamora NEW YORK, Aug 17 (Reuters) - Teachers face a harsh lesson as inflation drives up the cost of everything from paper to pencils before the school year begins, leading some to cut back on supplies - or substitute with cheaper items. A National Retail Federation survey in July found 47% of consumers were switching to cheaper options for school supplies due to higher prices.