Your API is not RESTful. URLs are supposed to identify resources, not operations. "Find by vehicle ID" is an operation, not a resource. I'd expect an URL like "/prices?vehicleId=2" or "/vehicles/2/price".
You're also no using HATEOAS correctly. The point is that except for the entry point of your API, you don't build URLs on your client side. You navigate by using the links returned from the service. You should have gotten a link to your endpoint in a previous operation.
Anyway, none of that has to do with your problem. Can you show use the Price class that the client uses?
Now, I wanted to find all the prices with a particular vehicleId so I added that findByVehicleId method to the PriceRepository (I thought that that's the way I need to do it) and now http://localhost:8082/prices gives me the following result: