Going rate for .co.uk surnames?

[SiusaidhSiusaidh is verified member.]

I noticed Henderson.co.uk attracted generous bids last week on UKBackorder. If you take a surname which is roughly in average usage numerically in the population, and NOT a major company name, what would you say is a typical going rate if it went to auction or some other means of sale? (Assume it does not already attract major traffic, and obviously I accept that selling any domains is to a considerable extent about who comes along.) Just a ballpark guestimate perhaps? £200? £500? £1000? I'm interested because I've had an offer on one.