That's completely relative. There was a spawn res they went for something crazy like 100 million. So... I would venture to say it's worth a bit.
Not just that but also, what res number it is, who owned it before, if there is anyone else at the time that wants that res, how much the people that want it can afford and how much you are willing to give it up for. Quite a few things ;-)
Utopia? They will have to be a gold supporter at least so that will probably make it worth about 3.5 or 3.75 Mil.
You're right. I just remembered it was a lot and now 5 mill doesn't seem like a ridiculous amount to me anymore xD it's still a lot though.
A friend of mine a year back bought a utopia one for 450k so I would value this one at around 1-1.2 million.