I have never done that...i think you have to be very carefull when doing so...first off, you have to make sure that you buy good quality vaccine and if they are properly kept and transported. If not, they will "go bad" and either have no effect on the body or even make them sick
Another thing is, make sure you know how each shot should be applied, some will be in the skin and others need to be in the muscle...so i would suggest doing your homework prior to attempting...it's always good to save money but make sure it is safe!