As far as I know sodium hypochlorite at any strength doesn't come in a powder form. Calcium hypochlorite is powder but not recommended for use with cleaning. Found out by trying it, really hard to dissolve. At $236.00 per 35 gal. seems high to me.I get 53 gal from Univar for around $200.00, and I'm pretty sure others here get it for a good bit cheaper even. Gotta do what you gotta do though. If your looking for small amounts go to Wal-Mart and buy a few cases of 6%, as you should never need it at 12.5% strength anyhow. (I've added a signature but it has yet to display)
Jeff