So I scanned through the above posts but didn't see some of the things that I do to save on shaving. First of all, I think that if you are someone for whom the MMM approach of using a hair trimmer in lieu of shaving works, you are probably really saving the most money. However, if you do love the coo of your significant other when they feel your shaven flesh, or you work in an oppressive environment where grown up hairs are not allowed then you will need to shave.
First, I really haven't optimized the razor acquisition side of all of this. I think I bought a pack of razors quite like this 2 years ago.
http://www.costco.com/Schick-Hydro-5-Blade-Razor-with-15-Refills.product.100087764.htmlI also use soap for my shave, which is a significant savings.
That said, I am only on my 7th blade (In 2 years) thus far, if you count the one in my travel kit as being used. Note that I shave only twice a week, because I am a grad student and I try not to spoil my wife too much :) The longevity really comes from two things.
First, keep the razor that you are actually using in olive oil between shaves. This appears to suspend the rusting process due to keeping water and oxygen from coming into contact with the metal. I have found that olive oil really does work well for this, and because it also tastes good on salads you probably have some in your house already. No need to buy anything fancy. Don't use canola oil though, that fried one of my blades.
Second, before each shave rub the blade against you palm in the opposite you would to shave. YOU SHOULD NOT BE CUTTING YOURSELF WHEN YOU DO THIS. I have never cut myself doing this, and I do it twice a week. I do this 20 times on each palm to make sure they are even. What this does it flatten out the blades of the razor, so that the cutting surface has no ridges or valleys. This allows the blade to continue to provide an even shave, and makes it less likely to slice into your skin.
That's it really. I think I picked those up in a reddit thread a while ago, and it really has payed off. So much so in fact that I am a little bummed that I have such an abundance of razors preventing me from trying out all of the cool suggestions previous posts have mentioned. Hope these help. Even if you have a silly expensive set up right now, finding a way to work these two things in can really create a lot of longevity for your shave.