To set up a price per quantity for your products in ERPAG, go to
Purchasing > Suppliers
Open the wanted supplier from the list. In the supplier price list section, you will see a 'Tier quantity' column.
Now, to set up price per quantity for a product that is added in the suppliers price list, you will just add the same product one more time, in the 'tier quantity' column you will type in the quantity for which you want to set up the price and in the 'purchase price' column you will type in the price for that quantity.
Once you save the changes, you can generate a purchase order for that supplier with just one click, by using the 'create' option on the right-hand menu.