First, you have to get his club to accept your bid. To achieve this, either make a very high bid (many times his market value) that the club cannot reject; or make an inquiry and accept the club's demands in return. When his club allows you to negotiate his contract, click to offer him a contract. While in the contract screen, click "News" on the left toolbar option (do not click the back arrow). Click on that player's name and withdraw your bid. Re-bid for free or whatever amount you wish. Click the back arrow on the left toolbar, this time back to the screen where you are discussing his contract details. Offer him a reasonable contract. When he accepts your contract, he will join your club on a free transfer (or the amount that you re-bid for).
When you need to pay a scout or coach a wage higher than the board would normally approve, select the "Approach To Sign" option. Change the person's default position from scout or coach to assistant manager. Change the offered wage to 0. Select the "Offer Contract" option. Wait until he rejects your offer. Select the "Approach To Sign" option again. That person's default position should still be assistant manager, with an increase in the wage limit that you can offer him. Choose the desired wage you wish to pay him, then offer that person a scout or coach position.
Play as Cardiff City and get promoted. In the first division, there are many players on a free transfer: Leonardo, Savio, and others. There is also a goalkeeper at Soi Plate who is class.