If it was that simple then no one would.
I think it is Ionics that do a domestic system something like (but not so 'Heath Robinson') you are talking about, you just connect to an outside tap (apologies to Ionics if I have that wrong
) and away you go.
If you are quite literally going to virtually manufacture your own system you will need some pretty specialist knowledge.
You can't leave aside the pump, brush and pole, that bit isn't cheap either
You can certainly buy a big DI tank to process your water, and I have seen a post by Justin Ruggles on how to work out how much pure water a given amount of resin will produce providing you have the TDS reading of your source water.
And you will really need to put in pre filters too.
No good just buying a bag of resin, you won't be able to make up your own resin tank and filter!
Ian