I am trying to build a calculator in excel which determines how much Luxury Car Tax, Stamp Duty, GST and Registration costs there are in a total Drive Away price showing all of these numbers with their respective titles and a final "cost price".

But it has me stumped

Working it out forwards is quite easy but moving backwards from total price and bringing the elements out is proving very difficult for me.

Here is why:

Stamp Duty is calculated at 2.5% of every $200 or part thereof if the price inc GST is below $57466 but moves up to 5% of every $200 or part thereof beyond the $57466 threshold.

Once past the $57466 threshold luxury car tax is calculated at 33% of every GST exclusive dollar beyond the $57466 threshold. BUT, if it is a Low Emission Vehicle the threshold moves up to $75375.

Registration is charged at $750 for a new car but it is only $32.90 for a demonstrator.

So you can see there are quite a few variables that are in the problem...

Please Help!!!