Haha. If I were to use a new blade every day I'd use Treets (1$ for 10 blades). Feathers can be cheep(er) if you buy them in boxes of 1000 from random asian-esq countries.
Haha. I thought the treats were pretty decent. I got an acceptable shave out of them no matter which type I used. Fortunately theyre are a couple blades that dont tug at all, so I dont get to use the cheapos. Unfortunately, the blades that dont tug are more expensive.
I change razors each day. They hang on racks on either side of my medicine cabinet. After I complete my shave for the day I remove the blade from the razor, rinse it off and then put it in the razor I will use the next day. That way I not only rotate my blades but also my razors. As for how many shaves from a blade, I keep track of that in the SOTD forums. Usually only 4 shaves per blade unless I am using a GEM then only two shaves.
I actually get significantly more shaves on my single edge razors. I attributed it to the thicker blades. I get 5 easily.
My Crystals will get me at least 4 shaves since I will typically 'spin' the razor as I shave. What I mean by that is I'll shave with the 'front' of the razor on one side of my face and then 'spin' it to the 'back' for more even blade wear. My shaves (unless I am lazy) are a minimum of 2 passes and my beard hair is VERY thick. I don't have experience with other blade times (Injector or whatever, but I did buy a Trac II for travel so we'll see how that goes) but I know that most DE blades I have tried have worked out in the 3-5 shave range. I am super light on the pressure though and my prep is very intensive so that all might help.