Excel 2007 : Stacked charts

Hi - I'm new to this forum and apologize if this has already been asked and answered several times. I'm trying to create a stacked chart, but with both values starting at zero, if that makes sense. A good example would be if something costs $5 and an upgrade to it is $7, for a total of $12. In this example, I'd have two lines - the first 'base price' and the second 'total price' of $5 and $12, respectively. In a typical stacked chart, that turns out $5 with $12 on top of it....is there a way to have the $12 start at zero as well so the base would be seen as $5 and the upgrade as $7? I suppose you could just do the formula and chart the difference, but it seems like there should be an easy way to do that...