It's like Bargain Hunt. Need two or more interested buyers to start a bidding war.
Ultimately, as David says, it's about what the market will pay. Many factors are in play there from the cost of comparable players to resale value. The World Cup helps raise profiles and interest which is why, if we are selling, we should take advantage of the uptick in publicity. Plus it's another success story we can point to when trying to sign new players.
While 3 or 4 million might feel low, it's a pretty good return on investment financially and for what has done for us on the pitch. I'm sure the Board will have run the numbers and figured out what is reasonable. I remember Caldwell quoting all the stats for Miller comparing him to similar players in his age group, and I'm sure they will be doing the same for all or potential transfers out.