Forum Discussion
Having been on both sides of this interaction, I can tell you that "volume discounts" may not be the terminology you wish to use.
You, and hopefully the client, are looking for a long-term mutually beneficial business relationship. As your relationship deepens you come to "know" your client better... their branding, their culture, their particular needs, their approval criteria, etc. The ability to provide even more appropriate solutions to their business problems, in less time, with less re-scoping and hassle is the result.
It is that result that may be worth quantifying with a lower rate for certain future projects. And that is how I would explain it - That as a valued partner you want to pass along the savings, monetary and otherwise, that come from having a long term relationship.
Otherwise you are competing on price alone.... and that is not a place you want to be in.