Dorkanglenumbers is full of crap.
Feral domestic animals in my area get their "shots" for free. 
We had a deluge of rats and feral cats when a nearby old housing area was demolished for a shopping center.
I have no clue how one even goes about catching a feral cat, let alone getting it to a vet. I let them hang around because of the rat problem, which they were quite efficient at dispatching.
Those where the spookiest cats. They were all gun metal grey with big gold eyes. They gave me the creeps just to look at them.