£130 would be about right for a branded one like Bosch. I don't think they cost differently to what Audi charges. The cheapest is a generic lambda probe for about £40. But you will need to wire your own plug and get the correct 4 or 5 wire version. I wouldn't bother with used item as they are a little bit like consumables. Think of them as clutch, brake pads and cambelt, they all have limited life. I believe mine is on the way out too, but since I use Shell v-power, the fault doesn't come up.