The first one. The quickest, as you don't have to download any kind of third-party software or files, all you need to have is some basic computer skills. It is about editing of save files. Good for us, save files are not encoded in some game's format, it is just a plain xml text. So, firstly you have to open a folder where your Farming Simulator's saves are in. Usually it is located in:
C:\Users\{PROFILE_NAME}\Documents\my games\FarmingSimulator2013
or
C:\Users\{PROFILE_NAME}\Documents\My Games\GIANTS Engine 5.0.1
There you will find another folder, bearing a name of your savegame. Open it and edit a file named "carreerSavegame.xml" using any text editor, Notepad for example. Look for "money" word, after which you will find "=" character. Right after it replace a number placed between quotations marks with a money value you want to have. You probably also should consider checking "loan" and some other statistic-related parameters.
The second is fairly simple. All you need to do is to download savegames with a rich deposit. By going to the previous link, you can choice a savegame file with a difficulity level of your liking with $50 millions.
The third is one is about using a special mods, designed to give a player an unfair advantage. It can be ridiculously big cargo size of your harvesters, unbelievably big profits or astonishingly small spendings. One example of such mod is Money Mod, where modmakers implemented an ability to gain lots of money by pressing a combinations of buttons.
Of course, you can use memory-editing utilities as ArtMoney or Cheat Engine, but taking in account the simplicity of methods above, it is entirely needless.