OpenAI's new price sheet has no bulk discount. The $20 plan buys 1x Codex usage, the $100 plan 5x, the $200 plan 10x and the $500 plan 25x, which comes to exactly $20 a unit on every rung. Until this week the $200 plan bought 20x. That was $10 a unit, half the price of every other rung. A $500 plan cannot sit above a $10-a-unit plan. At the old prices it would have been the worst deal on the sheet, since two $200 plans bought 40x for $400 and the $500 plan buys 25x. Both changes arrived…