Transfer fees (in 99% of cases) are paid over the length of contract not on an annual basis. For example if we pay 25 mill for Morgan and he is half way through his contract,we still owe Utd 12.5 mill in his transfer fee. So his book price is 12.5 mill, his value as an asset to Everton If we sell him to West Ham for 6,25 mill in the summer we still owe united 6.25 mill roughly. If we sell him for 15 mill we make a 2.5mill profit. This is the case with all of our players.
So in Gylfis case, we would have the annual liability to Swansea until the end of his contract that is dropping every year he is here. pretty much the same goes for the majority of players who we have signed recently, its why its so hard to shift them. We send them on loan for a year and their book price drops by another installment of their transfer fee and it might be easier to sell them in the next window. exceptions are the likes of Jamsey, Baines, Coleman and other lads who have been long enough to see their innital liability end. Young players that have come through the academy as well as they carry no book price and if sold are profit. Its always handy to have both of the afore mentioned categories at the club as it diverts funds to either new transfer fees or wages. Essentially we didnt hand Swansea 45mill, we are paying it off annually and over the course of his contract, we are two years into that, so we still owe Swansea money on his fee. If we sell him to make a profit we have to sell him for more of his liability to us, likely if sold him for 30 million we would make an 8-10 mill profit, not 30 million. Not including his wages.
As goat pointed out rightly, wages can sometimes make selling at a loss better in the long term, i think its better to be done very early in the contract myself. But at times if someone is on a big wage the wage liability may be more then crystallized loss, Klassen is an example of that, where we took a big crystallized loss on his fee to save the wage over his contract. Its not ideal and cant be done in multiple cases.
It works the other way as well and we actually have big lines of credit on our future transfer fees, namely on Rom and Stones fees expected from Utd and City. It went a long way to funding last summer in my opinion.
The above is why when lads write lists of if we sell so and so for such million and add it all together we will have 100 million to spend is worthless really. The worse thing you do is annual net and gross spend.