Julie,
I am weighing in a little late on this, but here are my thoughts.
My studio is a studio/gallery in a public place and as a service to my customers I provide framing. Basically that means that I frame all my own artwork and if people come in with framing requests I will accept the framing jobs on a limited basis, but I never advertise framing. Anyhow, I offer 20% off to artists and 25% off to my students. I don't really advertise the percentage off, but if I know someone is an artist I will mention it to them. I suggest that you ask different framers if they give a percentage off, and then recommend to your customers the ones who do. Because of overhead costs, I think that 20-25% off is fair.
You might also consider contacting a framing company and see if you can purchase frames wholesale. If they agree, you could choose 2 or 3 classic mouldings and get sample frame corners for those and then their catalogue for the other frames. That way you could sell the frames directly to your customer. Regence Picture has some wonderful frames that have been very well received by my customers. Their a tad pricey, but worth considering. Their website is:
http://www.regencepictureframes.com/
Mary