The APR wing would be cheaper and it is effective.
I run the GTC300 wing, and it puts 1058 lbs of downforce at 100mph. Its maybe actually just a little too much wing, as it has made me lose about 5mph top end on the long straight at Road Atlanta. I can however, keep the gas fully on in the esses now, so I'm really happy with it.
I got a great deal from Scott at Fontana Nissan