Open Cheat Engine on ps_game and search the exact value of the money from the character and if you have more values change it until you have 1 value, double click to save it down and "Find out what access this Address" and take an item from warehouse. you'll have more rows, select one, run tools/Auto Assemble, template/Code Injection and try to nop it, after File/Assign to current table and check it. See if the cost has been removed. I don't remember if it was only one nop or more, but i did it like this with the same CE experience you have.. so good luck and i hope other than explain you how to do it you'll learn more about CE
PS: If you are not sure about something google and youtube will help you! when you have the addresses to nop you can edit it on olllydbg and save it, so you don't have to do it all the time through CE.