-When you reach the part where you see the first helmet person, stop. After the intermission reload your ammo using the PC. Go out the way you came in. Shoot the raptors and keep switching screens so that more raptors will appear. Keep killing them while trying not to get hurt. Eventually exit through the same gate. if you did not get hit, you will get 6,000 or 2,000 extra points depending on your combo and how many you killed. Stock up an ammo and repeat. You will soon have enough money to by the EMP gun and ammo. The raptors will stop appearing after awhile -- go to a different place and do the same thing.
-While on the third energy disc, go back to your boat. Fight off the sea creatures, and go to the third energy plant. When you arrive, there will be a group of the sea creatures with the long necks. Boy the heavy machine gun and it will take only one shot to kill them. Do not get hit and exit the room after killing all that appear. You will earn 20,000 or 30,000 points. Repeat this in all the rooms from there on until you go underwater in the energy plant. You will have enough points for whatever you want for the rest of the game. If not, just return there and kill them all again.