Someone on another post compared vaccinating them for Makek's to vaccinating for polio. The odds of them getting Marek's is pretty low but it is devastating when they do. And like a lot of vaccinations, I've read it is possible to get Marek's from the vaccination, but the possibility is very low. You'll note I am referring to what I read as I am not sure of any of this.
I am getting my hatchery chicks vaccinated. Cackle has a $10 minimum for any number of chicks. They only charge about $0.10 or $0.12 each, but you have to really order a lot to get a volume discount. I don't know what other hatcheries do.
I do not plan to vaccinate any that I hatch. My thought is that with the large number of chicks handled by any large hatchery, there is a chance of exposure no matter how careful they are. With a closed flock, I can still get it from wild birds, but the odds are not very high. I'll take those chances.