He needs 48 pounds of flour because 12 x 4 = <<12*4=48>>48
He needs 4.8 bags of 10 pound bags because 48 / 10 = <<48/10=4.8>>4.8
He therefore needs to buy 5 bags of flour because 4 < 4.8 < 5
He spends $50 if he buys this flour because 5 x 10 = <<5*10=50>>50
He needs 4 bags of the 12-pound flour because 48 / 12 = <<48/12=4>>4
He would spend $52 on the 12-pound bags because 4 x 13 = 52
He spends $50 if he buys the cheapest flour because 50 < 52
#### 50