I think you'd be surprised how many high school kids might have a decent guns, fists, or weapons, rating. i don't think a +3 would happen often, but +1 to +2 can't actually be that rare depending on upbringing and geographic location/culture.
Pretty much any single vampire (normal template) should be able to be slain by a group of 3-5 players even with not so great combat skills.
Especially if someone has a hunting rifle, shotgun, or chainsaw. Neither of which would be 100% unreasonable to have somewhere in someone's house/garage.
The bigger issue is convincing someone to play the non combat oriented people in the neighborhood; if they know the game is a one shot, with the point of besting a vampire.