If they're interested, then they need to lodge a serious bid. I would say he is worth a minimum of 3m (Remember he was statistically the best player in the league before his injury), but I have a feeling that if they offered 1m+ then we would be forced into accepting it.
If you look at other centre-halfs in the league that are attracting interest, with the prices they are being touted at, we need to stay firm and only accept bids that are worthy of his quality. If the likes of Sean St Ledger (Quoted at 1.5m), Jack Hobbs (Quoted at 2m), Sol Bamba (Quoted at 3m), Andre Bikey (Quoted at 4m), Matt Mills (Quoted at 3.5m) are only available for their quoted prices, then surely we can expect to get around about that for Ben?
I know we aren't in the best financial position compared to the Reading's, Burnley's, Leicester's and Hull's of this league, but we should be able to at least hold out for a good fee. Maybe? Or am I being too optimistic?