Stick with what's working and don't change. It takes time and money to experiment to safe a little money, and in some cases you end up spending more in the process, and possibly going back to the original brand. I've only ever tried Rowasphos and it did wonders for me, eliminating pest algae and keeping the system in balance.
Other than the "no name" bulk brands, are other brands really much cheaper? I find the other so-call cheaper brand to be marginally cheaper and in some cases the same or even more expensive. This is why Rowasphos is staying with me for now. Mind you, I am only a part time user, one month on and one month off with just a couple inches in the reactor. I get wicked results using it this way. I tried it full time and it just makes corals looking a little pale. Maybe it's just my system, who knows??