You can sometimes have certain suppliers provide you with parts at a discounted rate.
There's no way to set this up on a supplier by supplier basis, however, you can utilise the "Local Purchase" within the parts discount code setup. This is done in Parts Managers Toolkit > Setup > Discount Codes
Once it has been configured against each discount code like about, when bringing parts into stock, change the drop down from "Stock Order Rate" to "Local Order Rate"