I would second the peroxide treatment. That's almost 100% assuredly your cheapest option.
You can also look for gluteraldahyde online, but in the concentration most often used, you have to pay for hazardous material shipping. Even then it costs around 1/20th of what Excel runs (note: it's not the same thing as excel, just very similar to the active ingredient, and is used as a hospital disinfectant, so you would have to use with Extreme Care).
I've been using it in several of my tanks for a week or so, and am already seeing increased growth in the vascular plants, and the algae seems to be taking a hit. From what I understand it can take several weeks of treatment before algae like bba starts to die completely.
I keep all kinds of plants, fish, and shrimp, and have seen no negative side effects, but I've heard that it will melt vals. YMMV.
Cliff