With that 5x logic any company trading at 10x profit would jump...

With that 5x logic any company trading at 10x profit would jump on it at 7-8x!
Completely nonsensical to suggest otherwise, Telstra could lob $600m at it and still be instantly earnings accretive, obviously that wont happen as they would want a discount as you suggest but 5x profits?
I think that $500m mark Bug came up with is slightly conservative as essentially we are talking an infrastructure asset.
For a non infrastructure play 7x profit would be suitable, being an infrastructure play (which it is because of the cable assets) I'd suggest 8-9x would be entirely sensible, especially to a company with a strong balance sheet and cheap longterm debt.