It's like asking how long your willy is.
What condition is it in?
How much use has it had?
Is it frayed at the edges, and a bit droopy?
How does it wash up?
How old is it?
What's the American v English willy exchange rate?
If I was after a top condition almost new 'Stich, I'd probably go to 600 quid, if it all matched up.
A slightly more bashed about one with a few crabs crawling on it, £250 or 300 max.
I paid 450 for mine about 7-8 years back, and it was the best money spent on my bike gear ever
So it all depends on how big and in what condition your willy is