1. Locate the savedata. It´s called "UserData.txt"
The location it´s in "SteamLibrary\steamapps\common\New Star GP"
Also you can go to the game, right-click on it, go to "Propierties" and the game files from there.

2. Backup UserData.txt in other location (in case something goes wrong)

3. Open the game and remember the number of Bux you have.

4. Close the game.

5. Open "UserData.txt" with the notepad, or just left-click on it.

6. Search the bux number you have. It´s close to the end of the file. Or do Ctrl+B and put exact number there.

7. Change the number next to Bux|I| to any high number... like 150000.

8. Save the file.

9. Open the game and enjoy.