Only problem with that method is if you're managing a club in a league with very weird rules for transfers within the league, says Chicago Fire in the MLS.
Another thing is that the ask value isn't an independent value. The game itself generates this value after considering contract years, contract value, squad status, club's financial health, manager ambition, player reputation, previous transfers between clubs, etc. The easiest to edit is player reputation. If you set that to a very low value (say 7), you can adjust askvalue and it'll stay a bit more constant. You can also use this to get players who wouldn't normally sign for your club.
Or you could edit a future free transfer and set the player to sign for your club on the following day.