#20 I use the Fusion blades. They last 1 month before I replace them. I clean them good and dry the blade. So my cost is about $3 a month.
Gillette Fusion 12 blades at $34
https://www.amazon.com/Gillette-Fusion-Manual-Razor-Refills/dp/B004B8AZH0?th=1
You can save more and get a really close shave with double edge razor blades but you will have to be very careful or your shave will be too close!
You can just stop shaving like these guys.
http://www.mrctv.org/sites/default/files/uploads/Brad/duckdynastyfam.jpg
I have a double edge razor which I have probably had for around 50 years. I had not used it in maybe 40 but around a year ago, I found a brand new pack of double edge blades which are name brand but no one knows how old they actually are.
I decided to try it out and to my surprise it gives perfectly acceptable shaves. Like you said, you have to be a little more careful.
Still the new ones do a little better so no point in using it but if I had to I could certainly live with it.
