I have spent a few days thinking about this now, and I am finding it difficult to come up with things under $50 or so that I would say genuinely improved my life quality. In fact, I don't know if there are many purchases I would say that about at all, but I suppose it depends how you define something "changing your life".
I do tend to save up (never buy on credit) and try to buy "the best" if it's not something I actually need right away, so that it's the last one of X that I am ever going to need to buy for the rest of my life - or at least as long as it's possible to reasonably expect something to last. Unless something untoward happens, I would expect my HHKB to last more than just a couple of years, for example.
This often (mistakenly) gives people the impression that I am loaded, but it's just that I don't tolerate crap, and have the patience to make do with what I already have, or go without something, until I can afford it. I put a lot of time into researching my purchases so that I don't rush into anything, and know what I should expect from them.
I've probably spent a couple of years lurking around keyboard forums before finally deciding on, having the money set aside for, and purchasing my HHKB2 Type-S for example.
What I often see on enthusiast forums (headphones, AV equipment, keyboards, computers etc.) is people that just slowly work their way up the ladder, buying something cheap and low-end to begin with, then gradually making more purchases in a never-ending upgrade cycle. Instead of buying a lot of things which I don't
really want, I'd rather wait and save up to buy the best - or at least the best that I can afford, or the product which best suits my needs (the best is not necessarily the most expensive) and something which I expect to last me a reasonable length of time, rather than buying whatever the latest overhyped product is because it's new and shiny.
Something where my purchase is outside the budget, but you can find items within that budget, was the switch to a
DE Safety Razor.
I have always hated shaving because I have very sensitive skin that would have razer burn or flare up after shaving no matter what. I have tried the most expensive electric shavers (irritates my skin, doesn't give good results) all kinds of other razors (with an increasing number of blades) all kinds of anti-irritation shaving foam, gel, aftershave etc.
Switching to a DE Safety Razor with Feather blades (which are by far the sharpest) means that I can get a
really close shave in a single pass, and using traditional shaving cream lathered with a brush instead of that gunk from a can, leaves me with no razor burn and little to no irritation. Replacement blades are also extremely cheap compared to Gillettes etc. even the generic brand, especially if you buy in bulk. For shaving cream, I like Truefitt & Hill which is somewhat expensive but if you're using a brush to build up lather, a tub should probably last you a long time (you need a lot less than you might think) and it has been the least irritating cream I have tried so far. This is not for anyone who is always in a rush out the door in the mornings though, I get up earlier to give myself an extra 10 minutes to take it slow (wrap a warm towel on your face for a couple of minutes before the shave like you would have done at a traditional barber's etc.) and it's made shaving something I look forward to now, rather than a chore.
And I don't know that I would say it improved my quality of life, but a Leatherman is always handy to have around. I keep a
Squirt S4 on my keyring, and end up using it all the time. The S4 is particularly useful, because you actually get a decent pair of sprung scissors unlike most multitools, which just have a crap pair of folding scissors. (even the scissors on my full-size Leatherman are much worse in comparison) It does mean that you do without pliers though, but none of the other small tools have a needlenose option, and I don't find regular pliers that small to be much use in my experience. I think the closest alternative is the Style CS, but it's a longer tool and I think it's also missing some of the features of the Squirt.
Really? iPhone charger disassembled... same pooy stuff as on DX.
Hm, contradicting evidence:
http://www.arcfn.com/2012/05/apple-iphone-charger-teardown-quality.html