The reward for surviving last winter’s frigid temperatures and record snowfall, several states are learning, is drastic price increases for road salt—in some cases, five times as expensive as last season.And that’s even if they can get it. Replenishing stockpiles is proving challenging, especially for some Midwestern states, after salt supplies were depleted to tame icy roads last winter. Price increases of at least 20 percent have been common in several cities, including Boston and Raleigh, North Carolina. …