% Increase formula

Hi Guys
I have 6 columns of prices from A1 TO A500.
I need to update these prices at different intervals by a percentage
Sometimes it could be 2% or 5% or whatever.
I would like to create a box at the base or top of each column that I can input the % increase I need.
I then want all the prices to update by that percentage. Can somebody help me with the formula and the best way to do this.
I am using 2007
Many Thanks.
Dodge

See attached file. change % in green cells and see result.

Thanks very much for that Van.
Can you show me the way of doing the increase to the base rate column without creating other columns showing the increase.
EG: Say the base rate is $100 in A1 Can I apply the increase to this column so it it changes the $100 to whatever the increase. And if I hit 0% it reverts back to $100. I can put a green box at the top of each column that I type my increase into.
Thanks Dodge