The problem is the “prijs” price field. I've checked one of the car pages, and that field is not numeric, therefore that filter always fails: https://i.imgur.com/l0CdOzf.png
For example: € 2.950 – MySQL cannot cast a field to numeric for BETWEEN operations if there is other than numbers and decimal points are present. In this case the correct value must be simply 2950
I recommend formatting the price in the output process, when printing the field value. It's much better, as you will be able to do queries based on prices.
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