My daughter bought her sweater vest for 4644 yen ($39.36 €35.72) at a special shop. She wears it under her school uniform. She also bought a long sleeve sweater for 7,128 yen ($60.41 €54.83) as her school clothes.
The below is a sample of school sweater vest (link to Amazon).
Here is a sample of school sweater (link to Amazon).