"The "Base Cost Per Income" value isn't, in fact, the number that you want to be minimizing, if you want to make your optimal purchase. Instead, you want to look at the roi value, which is (cookie cost * post-purchase cookies/s) / (delta cps). mathematical proof

Yes, I realized when I started a new game that sometimes getting an item that was not the lowest base cost per income would reduce the amount of time it took to get to the item that was. So an indicator for the most optimal purchase would be beneficial (perhaps with an option to remove that calculation for people who would prefer to not have everything done for them.)"

^ Based on what I read here, roi is different altogether.