get the child value of checkbox

I am having the following checkbox case and want to have the sum of value after the second comma. I am having many unchecked checkbox options to select. When I select an checkbox option then I want to have the value of selected checkbox after second comma. checkbox options are looking as below:

[x]Laptop,2,50.00
[x]Desktop,2,20.00
[]Keyboard,2,5.00

In above example, I should get the sum of 70 (50 + 20).

Can someone help me please where to start? Or is there a similar example to follow. thanks