Use cheat engine, it's really easy to use, just open the game, put your money value in the cheat engine and scan (it will detect many variables with that value), then you buy something to change your money, enter the new value and click next scan (the number of variables detected will decrease a lot), repeat until you got only few values scanned, double click they, change their value and apply, it will change your in-game money when you change the correct variable, then save your game and that's it. You can see some 5 min tutorial in youtube, it's really easy to use and works for every game that save the variables on your computer.
Also, I will give you another hint, when you are playing a game that you can find the "saves" somewhere in the archives (steam games doesn't have it, but simpler games do (rpg maker, booth games, html games, etc)), you can use the site "save edit" to change your variables inside the game, replace the save and then load.