I actually get all my Coke syrup product from a local chinese restaurant where I know the owner. She orders what I want in addition to what she needs, and I pay her for what I ordered. The best thing is that she gets a lower price the more she orders, so it benefits both of us.
You may want to consider a Breakmate, I have had one for a few years and I am very happy with it. It certainly is not as economical as a true fountain but it takes up a very small space and can probably be purchased for $300 or less. If you look at some of my pictures a the link below you can see mine:
So do you hold the button down and it dispenses until you let go or does it give a set amount of drink when you press the button?
You can either set it to small or large with the push of a button. That was one of my major concerns before purchase but I can tell you it has really worked out well. The small is about 3 oz and the large is about 6 oz. As I said before it probably isn't as economical as a true foutain but I know it has saved me in regards to waste. I have three younger kids and they have a lot of friends that hang out here and all know that I don't care how much pop they drink but they can only get it one small drink (3 oz) at a time. Prior to the Breakmate I would find 5 open cans of soda with about 3 oz drank out of them and the rest was waste, I don't have this situation anymore. It holds three flavors but I have got a bottle of vanilla syrup and cherry so we can have cherry coke, vanilla coke, cherry sprite, etc. Some of the models (mine included) also have a button for soda water so if you wanted to you could keep other syrup flavors around to make your own soda. We did this for a while but really didn't use it so I didn't replace any of the syrup as it got old.
Right now I have a maytag skybox. I am having the same problem that you had. The kids can't drink a whole can of soda and I really don't want them to either for that matter. So we have some decent waste. I am looking at adding a good bar gun and using the Maytag for specialty drinks that I can't get syrup for. e.g. Virgil's Root Beer.
I have thought about adding a breakmate for my office here. I don't think I want one in my theater room as I fear that the system will be a bit too noisy.