When it comes to shift kits you really need to know what your getting. The prices above explain about 3 different ways to go about shift kitting a gearbox.
There are many types of kits or mods you can do to make the gearbox shift harder. However there is also alot of other problems that should be fixed while there fitting a shift kit however some kits don't even drop the valve body out.
Ill explain the basics i different stages. (DIDO = Drive In Drive Out)
Stage 0.5
Pressure control modification when adjusting the pressure manual with sump off or installing an resistor into the path of the signal for the PCS. Look to spend $100 DIDO
Stage 1
Manual pressure adjust and boost valve fitment. Look to spend $150 to $200 DIDO
Stage 1.5
Boost valve and spring install, Drilled V/B Plate, Line Pressure spring install and Accumulator spring upgrades. Look to spend $200 to $300 DIDO
Stage 2
New Boost valve and Boost valve spring, New Drilled V/B Plate, New Line Pressure spring, New Accumulator springs, New 1-2 Shift valve, New Actuator Valve Spring, New Cut Back Valve Spring, and a heap of other small mods to help the trans last longer. Look to spend $400+ DIDO
Extra Areas to look into while things are out.
VR-On have really bad Lock-Up problems and can cause major failures if not fixed. There are a few valve kit that can be installed when fitting a shift kit with the valve body out.
Solenoids can be blocked or leaking from worn orings which can cause major failures and should be checked also if valve body is out.
Pressure switches on the valve body are always filled with crap and cause many different problems that can cause people to have a new trans when all that needs doing it having it cleaned or replaced.
So when it comes to having a shift kit fitted you have to ask yourself if your getting just getting a kit fitted or are you getting a Full Valve body Overhaul as well.
To drive into a Automatic Transmission Shop and drive out with a full Stage 2 kit and Corvette Servo with the Valve body overhaul i would look to spend $500-$600 Plus Faulty Electronic items. Now that price is for Sydney with rent being about $7000 a month so different areas will be cheaper.