hummmm... i have been using powder wheatgrass for about 5 years (its fantastic by the way - you will notice a real difference after around 1 month usage and then keep it up) and i have tried pretty much every product out there. Sweet wheat is okay but very expensive.. there is nothing to warrant paying so much. I recommend pines... http://www.pines.com or a new company selling in sachets who are really good: http://www.wheatgrassuk.com .
good luck - don't pay more than £20 for a months worth.