5% Discount For All Registered Customers

Hi Coders,



I am looking to give ALL my registered customers a 5% discount on ALL products either forever or for a limited time. Can people please quote me on how much you would charge to write in this code into my site, and how i could change this in the admin section. Please include:



1 - Cost



2 - How soon this could be completed.



Many thanks



Ben@seeingisbuying.com.