How to do vector calc for cost allocation

The problem seems simple to do it using for loop, but I wonder if there's an efficient way to do below calculation.

costPerTotalUnit
0-1:    100%
1-2:     50%
2-3:    10%
3-10:  0%
unit/   cumsum/    cost
0.5/    0.5/    0.5*100%
0.3/    0.8/    0.3*100%
0.9/    1.7/    0.2*100% + 0.7* 50%
0.2/    1.9/    0.2*50%
0.5/    2.4/    0.1*50% + 0.4*10%

To do total calculation, it can be done quickly per below.

cumsumTotalUnit = 2.4;
costPercent = max(min(cumsumTotalUnit-(0:10-1),1),0);
costRate = [1 .5 .1 zeros(1,7)];
totalCost= costPercent.* costRate 
 (= 1.54)

However I want to be able to obtain the cost for each unit purchase. Maybe somekind of backward allocation?

Thanks,

PT