Enter "MEGASAXON" at the New Career screen to get more money.
Hex edit
Begin a new career and save the game. Write down amount of money you have, convert it to hex string, break it onto two parts and switch their positions (example: 1000 > 03 E8 > E8 03). Use any hex editor to open the savegame file (it's in the "Leadfoot\Data\Saved Game" folder). Find your string and replace it with EA 60 for example to to get 60,000. Now, load your savegame.