If you are just raising ALK, and not CALC, you can go to Leslie's Pool Supply and get yourself a 5 lb bucket Alkalnity Up (Sodium Bi-Carbonate) for $12.99 or a 5 lb bucket of Soda Ash (Sodium Carbonate) for $15.99. It the same as the Alk part in BRS 2 part.
Bi-Carbonate is also the same as Baking Soda and you can turn Baking Soda into Sodium Bicarbonate by baking it. Randy Holmes-Farley has a good article called something on the order of a "Better Two Part Solution". Here is the article http://reefkeeping.com/issues/2006-02/rhf/index.php">http://reefkeeping.com/issues/2006-02/rhf/index.php</a>
Bi-Carbonate will initially lower your pH and then restabilize after 24-48 hours. Carbonate will raise your pH.