Eli Lilly announced Wednesday that a 70 percent price cut for its two best-selling insulin products, Humalog and Humulin, will take effect in the fourth quarter. Lilly also said it would reduce the list price of unbranded insulin from $82 to $25 per vial starting May 1, the lowest price for insulin taken by diabetics at mealtime and lower than Lilly’s 1999 Humalog sticker price. Eli Lilly also plans to improve a program that limits out-of-pocket costs to $35 a month for patients.