Hi, we vaccinated ours for Marek's in the first 24h after hatching. Hard to find the vaccine, a bit of a drive to a large feed store...kept it cool, then to room temp. We did the injection wrong location-wise (into wing skin), but later learned we should have lifted the chicks by the nape of the neck like a kitten, and injected subcutaneously into the tiny bit of extra neck skin, without risking injecting into more tender chick parts. Believe me...it can be stressful for newbies! It was a two person job for us...I'd try to get more advice...is there Marek's in your area?
I think it depends on what you are going to do with the chickens. If you are going to show, I would definately vaccinate. If you are going to be bringing outside birds into the flock (esp. adults), I think it's worth the $10 as well.
I get mine from Jeffers. This time of year I get an extra ice pack and the styrofoam cooler.