Ok, I came up with a formula.
For better or worse, here it is:
I looked around the net, and came with a mean 8x10 price. This was in the neighborhood of $125 matted. (which, BTW, apug-gallery.com seems to fit into well !). I then looked at my total costs for the project (paper, chems, etc). I did NOT include costs of the negative process, as these images were taken on my 'own' time. I then was left with two numbers. I took the average of the two, and came up with a ratio. I then applied this to all of the sizes the customer asked for. Basically, this came out to be 60% of most mean prices.
Granted, this comes out to be substancially less than most here would sell a print for. However, I feel that this organization provides the comunity with a great service, and I feel comfortable with the prices I setforth. Had this been a comercial group, I would have charged the mean prices, or perhaps more.