A bike. Poor people in underdeveloped countries can use it to get access to education and markets, while people from developed countries can ise it to keep healthy and reduce their environmental footprint
I was going to say that, but out of the 6 bikes in the garage none of them are under $100 even second hand.
In fact I would advise against getting a cheap shitty bike that isn't going to last. Spend the extra money, get something good. It's better for the environment and your wallet in the long run.
I've driven "good" bikes all my life. Aluminium frame, disc brakes, fancy suspension, 3x9 gears. That sort of thing.
Wanna know what my best biking experience was? Riding a steel frame, 3-speed dutch-style rental omafiets with no suspension and regular-ass brakes on a vacation. That thing was hella comfortable, sturdy as a brick and convenient.
If I lived in a not fully car-brained city where you can safely bike and was tight on money, I'd absolutely buy an old cheap used regular-ass steel frame bike with no frills and use the hell out of it until it's irreparably broken. You can leave that thing standing in the rain, locked with just a frame lock (or perhaps even no lock at all) all without worrying that it might get damaged or stolen because there isn't much to damage or steal in the first place.
I also don't see how buying a "good" bike in any way helps the environment when the alternative is re-using something that's already been built and successfully used before.
I love my 2000€ Brompton that I daily-drive but I'd be nearly as happy with a 100€ bike like I described above. You don't get more bike when you go above that price point, you only get a more fancy bike.
Oh I'm sure the one I rode cost a lot more than that, I just took that as an example for a super basic bicycle. Point being that this super basic one was better in many ways than the fancy one at home.
I was also not talking about getting a "good" omafiets either; that was, like, the whole point.
Steel vs. aluminum might very well depend on how big you are, and if you're a guy or gal.
I'm small and the weight difference between aluminum and steel is significant enough that I'll never go back to steel if I can help it. Basically, with aluminum I can carry groceries and such easier b/c the bike itself is lighter.
Large folks with lots of muscle might not see this difference, however.
Here in Germany you can get a second hand bike for free. In the UK I used to be able to get one for about 50£...My current one is quite fancy, and I got it for 180€, so I don't think it's impossible to find it cheap and good.
If you live in America, there are certainly a lot of things to consider on this point; mainly whether cycling in your area is even safe—obviously the ideal solution would be to move to an area with safer cycling, but that's not an option for everyone—and I'd much rather someone not cycle than die because their area has horrible roads for cycling and they didn't think about that. Check the safety of your area, and consider moving to a safer area for cycling if necessary (Or if you're in it for the long haul, consider pitching in the community and trying to lead it towards a safer cycling future)