Hello, i am new to Zoho and would like to use custom customer item numbers, and custom pricing. I would like to take what i can do in the AS/400 and do it in Zoho. Is that possible?

for example,

If i set my selling price as $5.00 each, but if a quantity of 50 is ordered it will be $4.00 each. And lets say a specific customer referrers to my item #1234 as their item#56405, is there a way to put this info in Zoho to better track inventory 

thank you in advance!