Last time I checked, GCG highflows were $1900, you can get a Garrett BB unit for cheaper than that, especially if you know somone who works for Repco (staff prices).
Probly one of my favourite mods was after having the front mount put on, I had a bit of lag, so i got my manifold cut and shut and now it faces forward which reduced piping by about 1 meter and basically got rid of any lag. But for the price of some of the purpose built manifolds of late, that would be another option. Also with the cut and shut, you need an aftermarket computer anyway cos it will lean out some cylinders, but the purpose built ones you dont.