Originally Posted by YooperBrew
Simply because many soda makers don't have a supply of co2 around. For keggers, yes, it's much simpler to force carb. But for the majority of soda makers who don't have a regulator, a co2 tank, etc, the yeast is the way to go.
One package of champange yeast is about $.79 cents.
A gas setup doesn't have to be expensive, and for me, it paid for itself on it's first use. Just keep your eye on ebay for a regulator. I got mine for $25 shipped. If you're not going to be making a ton of soda, you could go for a paintball tank which you can get for anywhere between $10-$20 shipped
. This tank will give you about 30 liters of soda and cost a few dollars to fill. You'll need a nut to connect the paintball sized tank to a standard regulator, which you can get from Williams.
So you're looking at somewhere between $50-$75 if you do your homework and shop around.