I looked at 5 different RO companies looking for a roughly a 4000 gallon per day unit last year. I purchased a XL-34A-216 system from Applied Membranes, Inc in Vista, CA. With dual water softner, extra filters, and frieght it was just over $8k. Of the the companies I talked with they seemed to be the most thorough. I know they were not the cheapest but seemed like better built units. So I still need to install my system but hopefully it works well for me.

At 7 gal per minute you would be looking at over 10,000 gal per day unit. If you are not irrigating everyday you might want to think about storage tanks to save some money on not as big of a RO unit. Granted if you are making DI water, I guess that is a magnet to contamination in storage acording to Saunders Machine Works.