I don't think you understand how car sales work tbh. Everyone above you has explained just why there needs to be a markup on cars, but it doesn't seem to be getting through. Don't forget people will haggle on price as well, so that £2,5K could suddenly become £1.5K, which then you need to take running costs out of and then what if it breaks and you need to fix it under warranty... Very quickly that money can turn into a loss if you've been unlucky.
If car sales was that easy to make a fortune on, then everyone would be doing it.