Air rifle.
Pretty cheap, so economically available to the majority of people (a decent gun starts at £600, each shot costs around 2 pence).
You just need a wind free 10 metre by 1 metre space to practice.
Not easy, but cheap to practice, and can be done at home if you have a long hallway.
It takes loads of practice to get right, but is possible, and there are few others in this Country who do it to an International standard.
After that, air pistol shooting (a little cheaper to buy the gun, and less space needed to practice).Harder I think than the rifle. Could be easier for others.
I dont think there are many others events that can be done at such a low cost, by virtually anyone – 20 stone bloaters could fire a rifle, though of course, if you are fit, you wont wobble about as much!