does it have to be done buy the vet or can i just buy it there and do it my self
I believe it is only sold by veterinarians. If you are "in good" with a Dr. they may let you buy enough for your dogs and do them yourself. You have to give the vaccine below the knee on the back leg and try to get it under the layer of fat to avoid a reaction. It is not exactly like a regular vaccine.
I think it was matt who had a incident with a rattler after the anti venom ill let him tell you about it.
It's actually not an anti venom it's a vaccine that builds antibodies before any bite, an anti-venom is used immediately after a bite.

We've seen dogs that have been vaccinated and then bitten by rattlers/copperheads and had literally no reaction. A tiny bit of swelling at the site of the bite and that's about it. I think it's a very good thing for dogs in high risk areas.