Uhh, plug wires alone will be more than 50-60 if you get ngk's or oem's right? What brand were you talking about?
Don't forget a new air filter.
Figure 10 bucks a piece for plugs, cap, rotor, air filter, and fuel filter. 30-40 for an O2 sensor? 60-80 for plug wires. Set your timing for free.
I personally use high octane gas cuz i get better mileage anyways with it so its worth it (~40mpg in the summer), plus I have my timing advanced to 15 degrees for a bit more power, so i have to use high octane.
It'll be worth it to drop the money on a tune up now if you're only gettin 19mpg. The money you'll save on gas will balance out and you're car will run better longer,