If they are flat disks, like you say, you may be able to have them carved out using a cnc router. This would give you some very fine tolerances on the flat surfaces of the disk as well as provide you with a way to engrave. This does a couple of things, 1, you could be running smoothly with your own equipment, for less then $1,500.00 upfront costs and you can test out your market before dumping thousands into a mold. If it were me, I would try to make a plastic part that is a bit more expensive. Your margins might be a bit higher. Instead of having to sell thousands before making a profit. If you wanted to inject using the machine I built. It takes roughly 4 minutes to do an injection. It is a hobby machine, but gives you the opportunity to see your product. I call it X-Ject hope this helps. I am working on molding injection molds out of epoxy. One of my customers hopes to have his product in stores in the next 3 weeks, he puts in a lot of sweat equity. I told him he should make something more expensive as well.
Kevin
http://www.backyardengineer.com