Mate, the best bulberator you will get is if you fork out the ridiculous price for a cream dispenser. Honestly, if you are a nang fiend and you are careful not to break it then its probably a worthwhile investment.
You can make one with some stuff you can get at Bunnings for under $15. Mr. White made an EXCELLENT thread on this in early 2008 which is the best guide on how to make your own I have ever come across.
http://www.bluelight.ru/vb/showthread.php?t=386002 Here is the link, fantastic thread. I made mine before he put the pics up an its got a second variation in there now too which wasn't initially. My design was the first one and it done alright by me, I still have it somewhere at a mates house.
Pretty much everything you could ever need to know about how to use recreationally is contained within that thread. The possible gap in information is that overuse can cause B12 deficiency, one of the first signs of this is numbness or tingling in the extremities. Also, for the majority of people it isn't likely to cause long term addiction but there are plenty of documented cases of it happening.
You want to avoid direct contact with the gas as it is VERY cold and can cause freeze burns, always inflate it into a balloon before inhaling. Also, be careful when hitting the balloon that you breathe some oxygen too, because when your huffing pure nitrous from a balloon your body is going without oxygen.
Finally, it is worth noting that chargers are only 99 or 99.9% pure. Fuck knows that the other .01-.1% is but if you have ever put a bulberator through much use and noticed the greasy stains that build up it is probably a fair assumption whatever it is is not healthy. I remember reading years ago someone suggested placing a cloth over the nozzle where you attach the balloon to filter some of the crap, I believe it was Splatt but I may be mistaken, I have never tried this myself but from a health point of view it is probably a good idea.