I don't know about others but when I first got into wet shaving specifically DE it was partially due to how damn expensive carts were getting per blade. I decided to do some comparisons to see if SE and injector blades stack up cost wise. My estimates are based upon how many shaves I can get out of a blade, pricing is in USD with shipping factored in for representative vendors. For DE blades I get 6 shaves on average same as an SE and for injectors 10 shaves on average. Which one is the most economical, well it will depend on upfront cost for starters. The larger the quantities the less price per shave would be expected so using my preferred blade which is a BIC Chrome Platinum that will be the basis of this. First up a 100 pack of Bic Chrome Platinum blades sold on amazon here this includes free shipping. https://www.amazon.com/dp/B00YH25IWM/?tag=thshde-20 6 shaves * 100 blades = 600 shaves per 100 pack Price of $14.99 / 600 shaves = approximately 2.5 cents per shave Now for 240 Personna ptfe coated stainless injector blades with the keys sold here by razorbladeco which include free shipping. https://www.razorbladeco.com/89-0043-coated-injector-blade-in-dispensers 10 shaves * 240 blades = 2400 shaves per 12 injector keys @20 blades per key Price of $52.00 / 2400 shaves = approximately 2.2 cents per shave Finally Gem ptfe coated stainless SE blades sold in 100 and 200 pack quantities by Connaught, price includes shipping to USA. https://connaughtshaving.com/gemss.html 6 shaves * 100 blades = 600 shaves per 100 pack Price of $18.24 / 600 shaves = approximately 3 cents per shave 6 shaves * 200 blades = 1200 shaves per 200 pack Price of $31.32 / 1200 shaves = approximately 2.6 cents per shave End result is if you want to buy in big enough quantities it is pretty much a wash on the cost per shave per blade for either of the 3 platforms using these blades here. Upfront costs DE will be the cheapest and should be the overall cheapest option if you go for blades in 100 packs that are cheaper than Bic blades like Voshkod blades for example which can be had for $6.98 for a 100 pack on amazon with free shipping. DE is still the cheapest option upfront and price per cost per shave when the 100 packs of blades are approximately $14 or less.