I bought my system from Ionics and I'd happily get another and recommend them.
Sure, the main Zero systems are not cheap, and have features I would not be bothered about. But their Pure2o range (which is sort of the budget range) is superb in my opinion.
I have a 400 litre pure2o system, it was a reasonable price - about £2,700 incl fitting as I remember, and I cannot fault it.
mine cost me about a grand.brand new 500L tank and frame including fitting and pumpbox with controller/battery,DI,etc.just as reliable plus i have an extra 100L!

the £1,700 saving bought me an xtreme 47,hot water heater,heavy duty hose reel and microbore,gas bottle,clx 4,various brushes and goosenecks.