Electronics in general is hard as it’s almost all made in china and the best you can do is find local resellers. Most towns will have small computer places. The only online one I know offhand is Memory Express. They don’t have everything, but do have the basics and have price matching.
Oh yeah, that makes sense. Corsair, Kingston and Timetec are all kind of in their one price ranges so you can’t really use that as a baseline to say it’s 3x more expensive. I think the issue is they have very little DDR3 RAM. They have far more choices in DDR4, so it would be easier to compare fairly. It’s hard to beat Amazon for selection, but hopefully you can find something that works for you elsewhere.