When creating Price Levels, users should have the option to choose if the data source to be marked up or marked down is the item Cost or the item Sell price. It should trivial to add one more variable to the Price Level setup page with a drop down box that allows the user to select Cost or Sales price as their basis in the calculation instead of the way it is now where a user can only use the Sale price in the calculation for customer price levels and Cost in the calculation for vendor price levels... This is not intuitive and does not work for many retail businesses, especially not in today's online environment with super tight margins.

As a example, a user should be able to set a price level called "Cost Plus 10". They should be able to set the calculation parameters as follows:
Name: Cost Plus 10
Type: Sales
Basis: Item Cost **** Add this variable ****
Item Rate: Markup
Percentage: 10%
Round Off To: Nevermind

Similarly, the addition of the Basis variable will allow users to create the same Sales price lists just as they are hard coded now...

Name: 10 Percent Off
Type: Sales
Basis: Item Sale Price **** Add this variable ****
Item Rate: Mardown
Percentage: 10%
Round Off To: Nevermind

Cost Plus pricing is essential to many retail segments and critical to low margin / highly competitive segments like auto parts! It becomes even more important for B2B when we are distributing a large variety of goods from different vendors, each with their own pricing model and margin structure.

Here is a very simple example of how the the current Price Level setup fails the needs of the modern retailer...
We buy Widgets from Supplier A with a margin of 20%.
We buy Doomaflitchets from Supplier B with a margin of 30%.
We buy Doohickeys from Supplier C with a magin of 10%.
We need to be able to offer discounts to wholesale customers and repeat customers. If we use the current Price list model and set a "Returning Customer" Price list as 10% off, you can see that for Supplier C's product we will be selling at cost, ultimately losing money after processing fees and overhead, but Supplier A and Supplier B will have some margin remaining. When you start compou ding this issue with hundreds of suppliers across 10's of thousands or hundreds of thousands of SKU's it becomes unmanageable to say the least and "Cost Plus" pricing become very important to ensure no products are sold below cost.

If you REALLY want to enhance the functionality of price lists, you could add an option to do some basic math operations to create price lists. For example:
Price List Value = (Cost - Sell)/2 + Cost
or
Price List Value = ((Cost-Sell)/3 + Cost)*1.03

I know, probably a sizable undertaking, but it would be a very powerful tool.