Budget forecast template

Hi guys, I was wondering what functions would help me make a budget that can be used to create all sorts of hypotheticals involving different variables. That's probably confusing so let me give an example. Say I set up a budget with three variables Items Sold, Price, and Revenue.

All I know how to do now would be to set it up so a single one of those can be calculated if I put in the variables of the other two. So I could calculate the price I would have to sell items at if I had certain revenue goals and a set inventory. What I want to be able to do is have the system be ?fluid so that it can solve for which ever variable is left empty.

Is this possible? Thanks.

I know that this isn't a workbook, but the way this pace calculator works is the way I'm hoping my excel worksheet can function.

http://www.coolrunning.com/engine/4/4_1/96.shtml

The fields are pace/distance/time
As long as you provide any two fields the third field will calculate for you.
In excel to do this I would have to set up three separate sets of cells to do this, at least with my current knowledge. Hopefully there is a way to make a formula+cell reference setup that lets me avoid that problem especially because I want to have a lot of variables.