woody not what you wanna hear but i think it'l cost a small fourtune water bill).
Probably someone will be able to give you weekly water bill, but i think it's 50% waste with merlin.
I'm in same boat as you; so have my 200 gpd ro a my parents place, 625 ltr static tank, it produces 27 ltr an hour, water pressure good 75 psi (no booster pump)
use 200 ltr day ave, so always got 2-3 days water in tank (parents not on water metre)
don't think it would be £10 a week water bill.
Have you got an understanding relative, if there not on water metre you could fill a tank i have in under 10 hrs i think. (with a MERLIN; takes over 23 hrs for me ro)
Or you could put a couple of rain butts in someone's garden and link with pipe; so one fills up then into the next.
Hope you sort out woody.
Plenty of helpful guys o here.
goodluck. lee