Feet Per Second, doesnt matter unless you're going to be doing long range shooting.
And air gun would work, but... If you're going to shoot an animal, please use a bigger gun so it doesnt suffer... I am an animal lover and wouldnt want them to suffer. I cant stop you from shooting them but I can stop you from making them suffer with a hot piece of led boiling in their stomach intestines for several minutes or even hours until they bleed to death.
Ah well I'll try anyway... Try to shoot targets (paper cutouts) or have a bud throw a can in the air and shoot that if you prefer a moving target.
I'm Native-American so I only believe in killing an animal if you are going to make full use of it (eat as much of it as possible, except for the bad parts of course, and use the hide, etc) not just killing for fun...
Anyway, go with a 22 I've seen them go for under 70 bucks.

And yeah 1800 meters is a fuckload. I want to use that when I join the Marines as a sharp shooter. That would be badass hoping the sheer force of the bullet flying by a targets head doesnt cause it to implode. :P J/K

Maybe tonight we'll fly so far away... We'll be lost before the dawn...