Looking up a single line from a portal
We are a small screen printer with many products. Are products are sold with quantity price breaks. Ex: 50 pcs. @ $3.00, 100 pcs. @ $2.85, etc. I currently store my pricing price brakes in a portal. My question is: When I go to input info into an invoice can I lookup just the single line in the portal that corresponds to the purchase quantity on the invoice? If not what is the preferred way to handle this. The examples I have viewed on the web deal with fixed prices for an item with no quantity price breaks.
Any help would be appreciated.