Since Leckie seems to be the only person currently offering this modification for the Hi-Power, he can pretty much name his price. Realize that there is a lot of cutting, welding, and blending going on...very labor intensive especially if it is done correctly.
The easiest way to get an answer would be to call Leckie and ask.
Just be seated when he answers. Austin Behlert charged $900 for the conversion back in 1983, and I can't imagine that the price has gone down in the last 16 years.