This is a different situation entirely, but what the hey...
Last year, a co-worker of mine was leaving the job, moving on to bigger, better things. I work with a bunch of musicians and one guy had the idea to write a song for this girl, a novelty type song highlighting things having to do with her and the company, funny memories, etc.
So we wrote and recorded the song and we gave her the CD on her last day. It was meant to be heard by just her and the people who musically contributed, but somehow it ended being played for the whole company. Everybody started requesting copies, a total of about 30 people wanted a CD. To make a long story short, I didn't really want to charge everybody for them, but the cost of discs and the labels, etc. start to add up, so I made all of the CD's and put out the announcement at work the day before I brought them in. I put the stack of CD's on a desk with a box next to it with a sign that read "The CD is free, but donations for packaging costs are greatly appreciated." Some people put in a couple bucks, most put in a five and a couple people left some blank CD-R's in the box. It worked out great.
Like I said, different situation, and probably not the best way for you to do it, but I guess my point is, when you don't come right out and set a price for something, I think most decent people will try to offer what they can, especially other musicians or those who know that you put some blood, sweat and tears into a product. Also, make it look as pro as you can. If it is a disc with a white paper label with handwriting on it, people will probably not want to pay for it.
Hope that helped in some odd way.
Brad