I seem to remember from my younger days that it is quite easy make 
hydrogen your self.  Just water and an electrical power source and a 
couple other items. Very flamible though and dangerous to have around.

Bob
 



Sean Breheny wrote:
> They do use hydrogen for some weather balloons. It is also even more
> buoyant (slightly).
>
> On Fri, Mar 26, 2010 at 5:12 AM, Alan B Pearce <Alan.B.Pearce@stfc.ac.uk> wrote:
>   
>>> Helium is very expensive. I once bough enough to fill three 1meter
>>> diameter balloons (total of about 1500 liters) and it cost about $25
>>> US. Another $20 or so for the tank rental. I'm sure it can be had for
>>> around 1/10th the price if you are a high-volume industrial user but
>>> this guy isn't.
>>>       
>> In that case I would be tempted to use hydrogen ...
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