I agree with Trev mate and I've bought a fair few models off you so I know where your coming from.
All I would say though is not many people would buy all 4 and I think that's the problem. It's only us hardcore collectors. For example if I was buying I would but the white one only therefore weighing out around £75 as I have seen them for that.
This way I'm buying the same model in 4 colours just to say I have them all. That's why I said I would have them in an ideal world but I have plenty of other models to buy before buying in essence the same model 4times.
After all that I would probably be a buyer at £200 and I don't expect you to accept that.