In my GoDaddy Pro account I have full access to a client (nonprofit) GoDaddy account that contains four domain names.
These names need to renewed, it would cost the client about $15 per year but since I have the Discount Domain Club I only pay $8.29.
Can I set this up so I pay the renewals at my rate?
You could just purchase the domains yourself and bill your clients. Or you can add their details to the payment method and billing address. I think this qualifies for your discount as it's through your account. Better check though.