does a 2007 pontiac g-6 3.5 liter need sparkplugs for tune up? Is this a fuel injector model

Yes it has spark plug,s,and yes it is fuel injected,and the tune up price would depend on just how much tune up you are doing,plug,s wires,coils,fuel injector,s,filters,pvc valve,and more.

You probably don't need new injectors (expensive) but the rest is pretty much standard if it has been a while since the components were last changed. Most likely about $200-$300 if done at a reputable shop.

Plugs and wires aren't anything to do yourself. If you're an amateur mechanic, I wouldn't mess with the fuel rails and injectors. But my wife can do plugso and wires, air filter and pcv valve herself. It's way simpler than you'd thing. The fuel filter is pretty easy too. You'll just get a little gas on you. LOL. Coils are not hard to change either just Google it