How do you get the best new winter tyres?

Hello, we are currently looking for new winter tyres for a BMW 5 Series E60. It should be 17″ original BMW rims and the tires should still have a good profile, and of course should not be too old. Are there cheap alternatives compared to the new purchase at the friendly one? Ebay is always such a thing, because you don’t know how good they are in reality still, besides there are always black sheep. In the past there was an accessory search at Mobile.de, which there is a Is there any other alternative? Does someone here happen to have new winter tyres that they no longer need (e.g. for change of foot)? Or do you have to buy new ones?