Purrley,
I did it with both of my girls, but they are quite large and they didn't even flinch. The chip itself is about the size of a grain of rice, so you definitely won't be able to see it. It is placed right at the scruff of the neck, sort of between the shoulder blades, if I remember correctly. I think $30 is very reasonable too because I paid $50 per dog to have mine done. I have not chosen to have the cats microchipped. Mimi stays so close to home, and Butter.....well, who would want him? I'm teasing about that last part, but I don't think there is any chance of people stealing my cats.
Our chips are AVID. I know there are others out there too. Maybe you can do some research through "Ask Jeeves" and get some answers that way. If you feel comfortable about it, after speaking with your vet, and researching a bit, I think I'd do it. Just in case.....
Logan