With iPhonebrowser or your file browser of choice go to:
/var/mobile/Applications/*find the Fieldrunners folder*
and edit any of the *.enemy files with a text editor.
The text file will look something like this:
light_soldier sprite=”unit_light_soldier.asc” health=”100″ healthBarOffset=”-22.0″ speed=”1.5″ score=”1000″ resources=”100″ damage=”1″ renderFirstUponDeath=”yes”
Some of the stuff is pretty self explanatory. Resources is how much money you get for each kill. Edit this and you can bank tons of money.