I just did a little googling, and the problem from what I can tell is that glass is typically screen printed.
I dont know if you are aware of how screen printing is done, while the process is pretty simple and straight forward to actually do, there is a lot of setup and tear down involved. My mom used to teach this to HS students (thats how I know). Screen printing used to be the typical method to get ink on a variety of things, including clothing, but due to the time involved with setup and tear down of screens and the fact that many screen setups were limited in the number of colors they could do, her equipment could do four colors. http://en.wikipedia.org/wiki/Screen_printing
The other option I have found is etching glass which is probably the most cost effective option: http://www.glassetchingsecrets.com/howtosteps.html
I have no experience with this, and more googling will probably give you more info.