Hello- I am one of the few sewing teachers left in public education. Do not buy anything very cheap, as these are considered a throw away machine.
I bought BabyLock Anna's for my classroom. They are a mechanical sewing machine, that goes on sale for about $200.00, and are very good. I have some that are 5 years old, and still working well. I do service them myself, with cleaning and oiling.
Do not buy beginner students anything electronic, because they won't hold up. I made the mistake of buying a medium priced electronic machine for my classroom, that only lasted 4 months before the bobbin case malfunctioned, and guess what? The store I bought it from wouldn't cover the expense.
Then they told me it was one of those throw away machines! I asked them why I wasn't informed prior to purchasing it, and all they could do was look at me.
One point that is very important is, will your child ever use the machine after just starting to sew. I've have some parents who spent a lot of money on a machine their child sewed on for a year, then they lost interest.
I recommend that a basic mechanical machine is a good start for any student, and if they love to sew, they can graduate to a more expensive machine when they are ready.