i think a lot of risk is in buying second hand,
the pumps - you can get flow jet an vyair new for about £60,
hose reals, gardiners new 35 or slightly better metal ones - pure freedom about 70
controllers , i'm not too sure about because i stopped using them.
second hand tanks are cheap on here and fabricators make the frames for 100
ro an pre filters are too risky to buy second hand as the membranes are so expensive
battery's can be delivered new for 75
however saying that this is on here where everyone knows everything about prices etc, i think maybe ebay or somewhere you may get a grand, i probably would when i first started, because in reality if your starting out this kit will make you a lot of money