I think it's the case that most people believe that any V6 omega is going to be an unreliable, uneconomical, bucket of 5H!T3 especially if it's cheap, so the best way to convince the few people in the market for one that yours is the best and will at least be reliable and not a bucket of Plop, is to conjure a massive price out of thin air, and hope that there's one (born everyday) for whom money is irrelevant.
That said. I only paid £525 for my high mileage 3.2 MV6 saloon, and yesterday was it's first RAC call out, (and due to wrong rear disc, so maintenance related not reliability related), I have had to throw money at it in the first year, wish bones, and cam cover gaskets and coil packs have pretty much made it a £1200 investment. Plus I still need a passenger rear door in Z20M petrol Blue.
If I were to do it all again, I'd know what I was getting myself into, but I'd still buy the one I did, because if you buy a 70K car, it's still going to need all that doing in the next couple of years anyway.