A complex SD Pricing Scenario

Here's an interesting Pricing Scenario

There are six items in a Sales order X,Y,Z in one group and A,B,C in another group. Groups are divided by the routes.
X,Y,Z belong to one route Z0001 and
A,B,C belong to another route Z0002

Now Price is is calculated not by the quantity but by the weight of each material.

The logic is

If the total weight of all the materials in a group is less than equal to 100gm, the price would be 10000 Rs.
If the total weight of all the materials in a group is more than 100gm then sum of the material weight should be multiplied by a fix price 150 to get the price i.e. if X+Y+Z= 200 then 200*150= 30000 Rs.

Same Logic applies for the another group of materials.

The story does not end here. When both the group prices are calculated system should sum both the group prices and give this as the final price of the Sales order.

Please do not tell me that use a routine. I'll appreciate if you can explain the routine logic in detail.