Another HN user suggested a bike that costs $650, almost three times what the Tesla bike costs. https://news.ycombinator.com/item?id=49003333

So no, I would not consider $225 "completely insane".

Disclaimer: I have no ties with, financial interest in, or own any products of Tesla.

We bought our kid a balance bike for £45, there is no need to go much above that price.

It depends what you do with such bikes. My son at 5 y.o. rode green trails in a bike park with a woom bike (not a balance bike), and I have seen other dads bring kids with balance bikes to bike parks.

If that is your objective you are ok to spend a few hundred dollars on a kid bike if that gives you the hope you will be saving a lot more than that from the dentist.

This said, a dad like me whose passion are expensive bikes, is very likely to be willing to spend a few hundreds on a kids bike, especially if you have more than one kid and you plan to pass the bike to the other son when the elder one outgrows it.

There is a significant jump in quality between a bike-shaped object at Walmart and a name-brand kid’s bike at your local bicycle shop. There is also a significant jump in price.

It is. Similar bikes are $40 on Amazon.