A bike is an investment in your own health, and an investment to try and motivate yourself to go on bike rides.
Sure there are $10 bikes that might work fine, likely with some repairs or a new back wheel. There are also $100 bikes that work fine as-is, though they will tend to be heavier, older, and prone to failure (for example, it comes with 12 year old worn tires or gears that hardly shift).
Many people who want to try cycling want to do so cheaply, and don’t have any bike-mechanical skills or tools, and are really only semi-motivated to give it a try. This is a recipe for failure. What happens when that old tire flats on the first ride, requiring a 9km walk home? The person gives up cycling forever.
Alternatively, the person who is already a cyclist, could buy that $10 bike and get good use out of it. Because he has the situation and knowledge to fix it up and use it appropriately. People that live downtown and need a cheap bike to get to work and back, or an activity.
People suggesting a $300 used bike are doing so from an informed position - that the best way to get into it, is through a solid low-cost base. A used aluminum bike with decent parts, which is still nothing special.
I actually accepted a free bike for my daughter. It looked fine, and seemed to work ok. I shouldn’t have accepted that free bike, because a POS bike is worse than no bike, for a little girl. It weighed more than her, and the pedals seized randomly when pedaling forward. It was a low-end bike bought from a big-box store perhaps 8-9 years ago.
So I get to feel guilty for bringing a bike to the dump (again, I don’t want to put it on the street for another little girl to get turned off cycling for life). And then went and bought a proper used bike. It cost $160. For a 5 year old. It’s aluminum, and the brand is Giant.
I read an article about a guy that bought a $2,000 e-mountain bike for his 6 year old son. The result is his son is ADDICTED to cycling. The e-assist makes him feel like a super-hero. The boy joins his dad on some fairly serious mountain bike trails, and he can keep up. It’s an awesome activity, fun for them both. He also makes a point that he isn’t particularly wealthy, but decided to try this and invest in his kids interest in cycling as an activity.
Guess that’s all I can post about it for now? Could go on…