This is a cool technique that I read about on Rodale's website, I've been wanting to try it for years.
Another technique that I do use, but I don't know that it actually spreads mycorhizae, is coloquially called 'fungal flats'. I have been told that it actually cultures actinomycetes, but in any case it seems to make plants happy. The recipe is as follolws:
2 parts high quality
compost
1 part high humate soils (alaska humisoil is a nationally available brand)
1 part worm castings
1/8 part humic acid
1/8 part oceanic hydrolysate
you mix the ingredients all together and then cover in a high humidity situation for 3-7 days. the medium will become covered with white fuzz and can be used to innoculate transplant holes, add to compost teas, or spread under mulch as a top dress.
I typically use 2 cups as a 'part' in the above recipe and put the resulting ~8 cup mixture into a planting tray with a humidity dome on it with any vents just cracked. Once the surface is fully white and fuzzy I either use little chunks as innoculant under transplants or use about 1/3 of a tray in a 50 gallon batch of tea.
Total cost per tray has to run under 5$, might be much less