The easy rule-of-thumb guide to whether a product is over priced is how much advertising they do. Gillette, and thus Gillette's customers, spend a shitload on TV advertising.
Of course, it is spread out over the number of customers....so say you see roughly the same number of glossy adverts for Ford Focus cars and for Alpha Romeos, yet on the road you see ten times as many Fords, you can estimate that a much larger chunk of the Alpha's price tag has been spent on marketing.
I use King of Shaves Azure blades (sadly discontinued and replaced by a much pricier version)- they work better than Gillette, yet are a 1/4 of the price, since they aren't advertised on television. I came to them because I had previously been impressed by King of Shaves shaving gel.
I wouldn't be surprised if Lidl or whoever offered some inexpensive yet just-as-good-as-Gillette razors - I'll have to try some out.
The onion knows it: http://www.theonion.com/blogpost/fuck-everything-were-doing-five-blades-11056
Would someone tell me how this happened? We were the fucking vanguard of shaving in this country. The Gillette Mach3 was the razor to own. Then the other guy came out with a three-blade razor. Were we scared? Hell, no. Because we hit back with a little thing called the Mach3Turbo. That's three blades and an aloe strip. For moisture. But you know what happened next? Shut up, I'm telling you what happened—the bastards went to four blades. Now we're standing around with our cocks in our hands, selling three blades and a strip. Moisture or no, suddenly we're the chumps. Well, fuck it. We're going to five blades.