if you have a small round and need something quick, you could use barrels and a backpack strapped to a trolley, off the top of my head this is what you will need, a lot of people do it this way :-)
prices are approximate
a tds meter -15
a ro system - 200
a di polishing vessel with resin - 30
backpack -140
male and female eznap connectors 10
clx 22 with a brush - 200
foldable trolly - 15
bungee chords -2
25 litre barrels - find from car washes
you will have to be able to lift and pour a barrel which is a pain, after a while