In the latest update we have introduced a new "Price Logic / Pricing Strategies" where you have the opportunity to configure your own pricing strategy based on the various parameters.
With this function you have ability of prioritising suppliers on several levels, see the example below. You can continue to use the existing scenarios or create a strategy of your own.
The settings will be made in admin; Price logic's > Cost price strategies, for editing the existing click on the label or click create to made your own.

For example: 

A) Priority-1
B) Stock
C) Priority-2
D) Price model

Cost price strategy example