This would really depend on exactly what the problem is. See your intake manifold is like 2 intakes in one. You have long runners for torque and low end power and short runners for high end power above 3000 rpm's. There are runner plates that open and close that direct the air flow into the engine either thru the long runners or short runners. This is controlled by a vacuum control solenoid which is turned on and off by the PCM(power train control module) Here is a pic of the system
See no. 8 and 9 in the above pic,these are the vacuum solenoids.
Now it could be something as simple as the clips that hold the arms from the solenoids to the intake broken or just a bad vacuum solenoid itself which is usually the problem.
Here is a closer pic of them
See no.1 in this pic
This would run most likely $200 to $300 if you had it done at a repair shop.
It could also be the plates stuck in the intake which you may be able to spray some WD40 on and loosen up by hand.
Worst case could be intake or PCM which could run up to $1000 or more.