Starsan's the most cost effective sanitizer out there, a large bottke lasts me about a year and a half. And I probably brew a lot more than you do.
If you're having issues where it's cost effective, then
you're not using effectively.
Starsan is really a good investment, you only need to use a little bit at a time (you don't need to make 5 gallons of it every time- I usually only make 2-2.5 gallons on a typical brewday.) You can store it and reuse it quite a few times, especially if you use distilled water and store it in an airtight container. A lot of us store some in a spray bottle for all the little sanitizations we might need to do, like take grav readings. Some folks store a gallon of it and use that til the PH changes. (Get a 1 gallon jug of distilled water, pour a little out, and add a few MLs of starsan and shake. Just pour it back in and seal the jug.
Since it's a wet contact/no rinse sanitizer, you just need to put a gallon or two in your fermenter for example and swirl it around to make contact and then pour it back into your storage container...
With all the re-usability and versatility of it, it really is cost effectives, it works out to pennys per use...
There's a lot of great info in this thread, including the links to podcasts about the two most effective sanitizers we use, iodophor and starsan.
Sanitizer Question.