Workbooks supports the use of Pricing Schemes (and supply schemes) for Business users.

To create a Pricing Scheme, first create a record for your Product (Start > Marketing > Products > New Product) or open an existing Product.  Within the Pricing Schemes tab, click Add Pricing Scheme.

Give the scheme a name and complete the other fields.  If your Pricing Scheme is for a set period of time, you can specify this using the Start and Expiry fields.  

The screenshot below shows how you could enter different prices for different quantities of a product.  (Click to enlarge.)

To use a Pricing Scheme in a Transaction Document, ensure that you've activated the Pricing Scheme column in the Line Item grid.  Add your product as a normal.  This will pull through the default price/cost (if these were entered on the Product record).  In the Pricing Scheme column select the appropriate scheme. This will pull through the price information set up for that Pricing Scheme, overwriting any default figures.  The screenshot below shows a Quotation, which contains three line items for the same Product but with a different Pricing Scheme applied.  (Click to enlarge.)

Hope that helps.