Hi Warren,
I have a 400l tank in my van, and a 300gpd RO-man unit in my shed, which runs all day filling my 1000l IBC. I transfer the pure water to my van via a Draper submersible pump. (Only need a quick burst of pump as I've set the IBC up on a plinth so the water runs by syphon).
The RO-man unit cost about £300, with renewable prefilters at about £40-50 every six months. My tap water is about 280-300 ppm.
I've had the unit for about twenty months and it still produces water at 2-4 ppm. I then run it through an 18inch DI vessel. I've only had to change the resin in the vessel once in all the time I've had the RO.
The RO came with a pump, and I used the pump until a few weeks ago, then it broke. Now I just let the system work on the mains water pressure (about 35-40psi) and it works fine.
Cheers
Ian