If you smoke less, you'll save more. Simple as that, really. I do love a good joint, but nowadays I treat it more as a delicacy and almost always smoke out of a bowl or (moreso lately) a one-hitter. I can't give you a scientific answer about how much product is wasted through "sidestream smoke" (I like that term, btw), but it seems logical to suggest that some is; how much, I couldn't say.
I will say that, ever since I stopped rolling joints, I can make a half last upwards 6-8 weeks. I get plenty high everyday, for the record. Joints are useful for public settings, due to the lack of paraphernalia, and they are fun for group situations, but lately I've kept my tolerance down and my finances up through this means.