Mr. Puff is right. Costco and the like are the cheapest way to get baking soda. Not pool places, not industrial supplies. Costco.
If you use soda in your blasting cabinet, your vacuum could plug quickly as Milt mentions. This simple looking doo-hicky helps. It goes between your cabinet and vacuum. It attaches to a bucket. basically it takes the heavy particles out before reaching the vacuum. The vacuum still clogs but at a much slower rate. As the ebay add mentions adding water also helps.
http://cgi.ebay.com/Mini-Dust-Collector-Separator-2-Stage-Cyclone-Adapter_W0QQitemZ270269784158QQihZ017QQcategoryZ42 283QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Soda blasting does not cause any corriosion, don't know where that is coming from. Any metal after blasting will rust if there is any humidity. You need to use a product to coat your blasted parts. I beleive when places blast your car frame they recommend a process like this.
You should not use sand in any way for blasting. It's extremely dangerous for your health (causes similar health problems as asbestos).
A cheap material for blasting is coal slag. A 80 lb is $30 at industrial supplies places. It's more aggressive than soda, it does remove some metal but it lasts longer than soda and it etches the metal for better adhesion of paint and/or powdercoating.
In the picture below the black part of the bracket is original, lower left is soda blasted, the right bracket is blasted with coal slag.
