I bought the backspace/offset tool from www.thewheelfit.com. The model I purchased is the Wheel Fit Pro 45 and it retails for $399.00.
If memory serves me correct I found some discount code or mentioned some advertisement and received a promotional price of somewhere around $360 when I ordered it.
If you need any further information please let me know.
P.S. I just did the backspace conversion math on the Foose Design offset for his rear wheel at 6mm and came up with a backspacing of 6.24 inches. I also did the math on his front wheels (based on the 18x8 wheel) and came up with the same offset of 19mm. What does this mean – I have no idea but I just thought I would see if their math matched my math calculations.