To get 800 credits:
 
 Edit the mission files with a Hex editor and make the changes
 detailed in the table below to increase the number of credits you
 have to 800. This should be plenty as if you were to spend more
 you would be too heavily weighed down and you'd lose lots of
 action points.
 
 File    Starting Offset     Type:
 1       Hex 2309            20 03 20 03 20 03 20 03
 2       Hex 2309            20 03 20 03 20 03 20 03 20 03 20 03 20 03
 3       Hex 2309            20 03 20 03 20 03 20 03 20 03 20 03 20 03
 4       Hex 2309            20 03 20 03 20 03 20 03 20 03 20 03 20 03
 5       Hex 2309            20 03 20 03 20 03 20 03 20 03 20 03 20 03