^^$300 to install some plugs and wires???? NO WAY!!! That's a total rip off! Definitely do it yourself and come on the board to ask questions if you get stuck. There are A LOT of well experienced people here who could help you. Furthermore, those step-by-step instructions basically tell you everything you need to know as far as replacing your plugs go. Just remember to number your bolts as you take them off and don't drop any nuts (I dropped 1 into the engine bay somewhere and had this bright idea of dropping the other one to find out where the first one fell and ended up not being able to find either of them
LOL).