Estimating value of services and agreeing on amount to be paid for these services is at the core of what each consulting organisation does. And typically price negotiations are needed to arrive at mutually acceptable amount.
The easiest way to provide a discount in PSA is to use custom pricing and discount rates for various roles (such as your Junior Consultant, Senior Consultant and Project Manager). The downside of using that approach is that clients will make a note of the discounted rate and will not want to pay more for the same role and/or resource on subsequent projects.
There are other ways of making the figure on your quote lower that do not affect rates in the future. Rather than cut down on rates, consider some other available options!