Whilst I agree that Apple prices are far far too high for a DIY product it is possibly close to what a top PC repairer would charge to fit new RAM modules.
I liken Apple service (rightly or wrongly) to motor industry service prices, you can pay Mercedes prices, Ford prices or your local back street garage prices. Those in the know or with the time or inclination to gain the knowledge will probably tell you the back street, or Crucial price, is the one to go for. But there will always be those who feel more secure receiving service or parts from Apple (or Mercedes) because that is what they feel more secure with and/or able to afford.
I, probably you, and many others here will feel that, though they are not experts, are able to carry out some DIY upgrades or modifications and so can take advantage of free or cheaper products. Many things in life are easy if you know how but there is room also for those not so wily in technological matters to pay higher prices, thus all are happy and keep the wheels of industry turning and many employed.