Simple Save Editor 1.0 is pretty easy.
Click File-> Open, go to your save game in My Documents/My Games/Freelancer/Accts/SinglePlayer and whatever save is there which you want to edit. Then scroll down to where it says money = and change it to whatever you want. Click File->Save and your done

www.ioncross.com . Under Software, get the IONCROSS Freelancer Savegame Editor (or something similar - you'll know it when you see it). Best program I've ever seen to do it with - created by a god, Joe Boomz.

You can get the IONCROSS programs here at Lancers Reactor...

For editing Multiplayer games use the IONCROSS Freelancer Server Operator mk.V by JoeBoomz

For editing Singleplayer games use the IONCROSS Freelancer Character Editor mk.V by JoeBoomz

Both of these programs can edit a saved game...
you can edit the following...

ship
power plant
engine
shield
forward hard points
turrets
equipment
lights
cargo
location
factions
AND money
**** EDIT CAREFULLY AND BACK UP YOUR FILES! ****