Players are less like perfectly competitive goods you'd buy in a shop and more like buying houses or something. It depends heavily on the market, on how desperate the person is to sell, on things like the prestige of a certain player, on utility. You could argue that, on the final day of the transfer deadline, with uncertainty over whether fletch will play again, our utility of bringing in a CM goes through the roof since we are low on options and this is our last chance. On the other side of the coin, for a team like Everton who can't replace Fellaini with a player of the same quality, that puts a premium on the player. My parents got held to ransom over buying my family home about ten years ago I remember, because it was a situation where they were renting and houses were in hot demand, meaning that if you put it off you had to wait months for a new opportunity in which time house prices go up again. Yes, Woody got held to ransom over a few million for the Felli deal, but he made a decision that having Felli in the team this year was better than waiting until next summer to fill the gap in the squad. Lots of stuff in play here, and since we can afford it (ie. the Glazers might end up using this spare money to pay dividends in the end), Moyes making the signing being held a few million to ransom might end up being the right deal
Yes Value for Money is a different thing altogether. It's nice when you get value for money obviously, but sometimes it should take a back seat. People have been trying to hold united to ransom for years, Everton and Spurs are two clubs that are excellent at getting good fees for their players. Look at Lescott for 23m 5 years ago. Torres for 50m. Bale for 90m. Its a tough market place and sometimes you have to forget about value for money to get the players that are available