If you offer tiered pricing for your goods, we advise that you treat each tier as its own individual Product within your account.
Headshot (quantities 1-5) priced at $200/each would be its own item
Headshot (quantities 6-10) priced at $175/each would a second item
Headshots (quantities 11-15) priced at $150/each would be a third item and so on and so forth.
When you build out your Quote, you could insert these Products under the "Choose Any" option and preset the applicable quantities for each line item.
This would allow your client to select the proper price tier and then type in the quantity that they would like.
KeyWordSearch: Variable Pricing, Tiers, Quotes, Quantity