Sorry to disappoint, but valuations of £8M are way over the mark. When was the last time a CB, no matter how highly rated, went for anywhere near that much? Let alone from a Championship team. Comparisons with Walcott/Bale/AOC aren't valid I'm afraid as firstly they each play in more attacking positions, which are always worth more, and secondly Southampton can command a higher fee because of their reputation for developing young players. We can't, not yet.
Anything close to £3-4M and I can see us accepting it if Dunk wants to go.