I would not use the vaue of '$20.00" but rather enter the optional value for the combo box as just a number and then set the format of field2 to the Number format with 2 decimal places and the dollar currency symbol.
One can load the combo box from an array of choices and values. So if you have multiple combo boxes with the same choices and values each could be loaded from the same array. seItems
JavaScript can walk through an array so a vlookup type function could be written or one could use the index of the selected item to locate a cell in array.