That's fun, I recently finished repainting mine (I had more rust and crapier paint on mine). I went down to a car paint store and got some white and creamy brown paint, and did a two tone paint job that I hope to some day finish into a generic root beer theme (the painting is done, I just have to do that artwork and shine the aluminum parts).
I have had it in my kitchen for quite a while now (works great, just doesn't look as good as it will some day). I have been thinking of just buying the Frosty Rootbeer art from that soda-machine.com site so I can finally get it finished, but I really should just work on some custom stuff.
You can find IBC root beer at pretty much any grocery store in the bottles, and they usually will have orange cream, grape, orange, and cream soda too (I've found other random flavors in stores, usually not a regular item, on special and such). Sams Club has the best deal on IBC roob beer (like $5 for a case, fills 4 shelves on my machine). I actually use more bottled water than anything in mine (Sams Club sells the Nestle Pure Life 32 pack for like $4, usually get a few of those when I pick up the IBC root beer). I get kinda burnt out on soda, and really like just having the water in there (keeps it really cold, better than my fridge).
I have no idea how much it costs to run my machine (my wife actually handles the bills, and I've never asked her how much our bill jumped when we plugged it in). I also have a Ugonline Granita (slushee) machine going 24/7 (that was a great find). So those along with the arcade and pinball machine, it's hard to tell how much just one of those machines costs to run.
Good luck with your machine, and now that you have it, I'm sure you'll have no problem finding soda for it (after I bought mine, I became keenly aware of every stores "soda situation").