You get less money for everything in the game. It's the 80's, though. Before the inflation for GTA3. (joking).
The Hunter is an Apache-type assault helicopter. Large, green, mean looking, and makes a serious it-means-business sound as soon as you hop in and the blades start churning. It's armed with a machine gun and rockets.
It took me a while to be able to hit anything with it and not slam into the ground or blow myself up, but I figured it out and used it to get to the level 12 vigilante missions (big tip, press down L3--the horn button usually--and it'll level out into a hover if you get in trouble)
By the way, the Sea Sparrow also has a gun. I didn't realize that until I hit the R1 button by mistake and it started firing.