It's not the game as much as it's the way we all approach signings as managers. When there are only a few top players that you want to sign immediately, you can expect to pay huge transfer fees if that person is important to a highly successful club; this isn't unrealistic at all.
The AI teams won't pay ridiculous fees because they aren't focused solely on buying the top 5 best players at each position, who are stars at their club, like we often are. There are literally hundreds of players who would be adequate upgrades at reasonable fees, or prospects for the future, but we tend to be impatient and we don't want to build our squad slowly (and realistically) over 5-10 seasons. If you are not playing as Man City you need to look to guys from smaller clubs, or unneeded players who will strengthen your squad, not stars from top 4 premier league teams. Or find guys who want to join a larger club, for example Yoann Gourcuff who is easily one of the best players in the game, always wants to leave Bordeaux and you will get him for less than 20m.
Liverpool's default asking price for Johnson is 80m by the way, a bit high yes, but this is based on Liverpool not needing transfer money to buy other players, and Johnson being important and happy to stay. Rafinha is a very good right back for 10-15m and there are lots of other good ones for less:wub:
edit: just wanted to add, I just checked out of curiosity in my save in 2014 and interestingly enough, Johnson is transfer listed for 900k