I get where you are coming from. There are a couple of glaring issues with your recommendation of a cheap USB hub.
1. No Power Button
Having used a similar setup with my kids for awhile now, the lack of a power on button in a USB hub vs a real dock has a negative impact.
2. No Ethernet
Maybe people don't care about this anymore with his fast Wi-Fi has become, but as someone who works with many large digital assets, I still prefer to have Ethernet for anything sitting on a desk.
3. Desk Space
Unless you don't intend to use a monitor, have extra desk space, or intend to buy a monitor stand that you can fit the Chromebook and the USB hub underneath, then a Chromebox or alternative mini PC (nuc, Mac mini, Asus, beelink) gives you way more bang for the square inches.