Shaving is too expensive and is a demonstrative example of how most consumer products are designed to extract more money from you rather than to improve your life, or the world, or to be in any way remotely good.
and replacement heads cost in the region of £1.75. Gillette claim that each blade can be used for 15 shaves. This sounds pretty optimistic to me. But who knows. If you shave daily this implies a cost of 87 pence weekly, or around 45 pounds annually. This also means that the razor body effectively costs about 5 pounds, and is probably a loss leader.
Before this style of razor became popular, most people used what is known as a double edged razor. The bodies of these razors seem to be generally more expensive: a good quality one might be around £40. Though you can pay more, or less. The blades are significantly much cheaper. Blades can be had for £0.08 pence each. These blades are probably good for something like 3 to 5 shaves. Let's say 3 to make this as generous to gilette as possible. Assuming daily shaving that gives us a cost of 18 pence weekly, or about 10 pounds annually.
So we see a slightly larger initial outset, which is quickly dominated by the higher ongoing cost of the typical modern razor. If you expect that you will continue shaving for a year, then it is more cost effective to use a double edged razor.