Star san doesn't stain my equipment, the foam can be a PIA sometimes, but I don't usually worry about it.
Cost on sanitizer is negligible, if you want clean/sanitized equipment you will pay for it, as for keeping Star-San around for months, unless you are testing the Ph, which requires an additional cost in Ph strips or meters, a 32 oz bottle will make 160 gallons of sanitizer, who cares about 15 bucks or so.
If you brewed 5 gallons a day and used 5 gallons of Star san per day it would last over a month!
+1 to spray bottles of the stuff too! I can pretty much sanitize all of my equipment with a spray bottle!