Loads of variables m8 such as TDS of water, how much you need per day, how high you need to reach.....
But if you budget for £1000 for cheapo get you started then you will have some change.
£1500 will get you a much better quality of setup and £3000 for a WOW will I really eed to use all that high quality high reach stuff...
Best thing first is to invest a few £ in a TDS meter and find out how good or bad your tap water is. That will tell you wether you need an RO only, DI only or both for filtering the tap water.
Then its a case of working out how high you need to go. That will tell you how many poles you will need.
Then roughly what your trad daily target is will help to work ouwhat size tank and size of production unit you would need.
Add on a few extra £s for pump, hose, reel. Then little extras like pump controller, backpack. It can actually be done for closer to £500 but that wouldn't really be much of a system.
Look on some of the sites that sell complete systems to get an idea of top end prices. They do cost a bit more than finding and fitting the stuff yourself but it does take all that hassle away from you.
Regards
Mr H