Can't go wrong with 450 for that. Along as there's no damage to the major components (frame cracks etc).
Even if it needs replacement wear parts it's a good price for you, he'll be less pleased about letting a 1750 quid bike go for 450....... But that's how the market is!
New chain, cassette, chainring(s), cables, brake pads (depending on what it needs) will give you several more years service.