I may get flamed for this, but buy what you can afford and upgrade later if you need to. I started with the rock bottom bargain turd from ebay that was like $95 shipped. It kept my TDS at zero with a 100gallon system for about 9 months. I then added an add on canister refillable DI and put in new DI and it went back to zero. Eventually I replaced the RO membrane with a nicer Dow 75GPD. Still at zero. I've read all the arguments on RO/DI about you get what you pay for, but this is one area that I don't believe it. I still have less in mine than what I could get one from BFS or AWI. Now I got no support, but I didn't care since I knew what I needed to know. If you want the personal support go with BFS. If you want to be able to drop kick your set up go with BFS. But if all you can afford is the el cheapo from ebay, it is still 100000% better than tap and as long as you don't score touch downs and spike it on the ground it will last forever.
Joe