Yes, baking soda is 50 cents a pound at Aldis , Save a Lot or other discount grocery stores.
I'm using Peladow right now........its under $20 for a 50 lb. bag.
You can dose Randy's Mg recipe also, but my Mg stays up with my water changes, so I don't dose Mg.
I've never used the commercial brands as I went right from a calcium reactor to Randys two part and never had any reason to change.
Here is my tank thread--
http://reef2reef.com/threads/big-e-rimless-80g-sps.206607/page-2
I have a ton of growth shots in this thread--
http://reefcentral.com/forums/showthread.php?t=2197142&page=12