The devs are doing wrong one thing there about how much you need to upgrade. It is like they missunderstood. I suggest you to change how much you upgrade from ilvl 236 to 272. You just cant upgrade 475 valor from ilvl 236 to 272 with same cost of valor and it should be cheaper because it starts ilvl 236.
Maybe, start with 50 valor from ilvl 236 to 239, 100 valor 239-242, 150 valor 242-246 and move on.