It really depends on where you get the parts and what parts you use. But, you can get Autolite copper core plugs, about $1.50 each. New OEM wires will run you about $30 - 40. Might as well change the air filter and fuel filter which may run you about $10 each or there abouts.

I guess if you wanted to go the extra mile and dont know what the maintenance history on it is, probably wouldnt hurt to change out the O2 sensor.