form fields calculator

is there any good example to make a javascript calculator which can calculate te total sum from quantity fields and checkboxes? for example i have to lines of data, each can have different quantity and 2 checkbox. increasing the quantity will increase the sum 10 EUR (for one line, second can have different sum), checking some checkboxes will increases the total sum too, but also all the checkboxes may have different sums, like 5 EUR, 0,5 EUR, 2,49 EUR etc

some examples?