You need to use distilled or deionized water only for the last bath, the "final rinse". If your tap water is of normal quality it should be perfectly fine for all other baths. You can reuse your final rinse several times (you are supposed to wash the film very well to remove any residue of fixer, and if you do it you will also avoid contaminating your final rinse so that you can reuse it).

Rome water is quite problematic as far as calcium deposits are concerned, but I never have had any water mark problem as I prepare the last bath with cheap water for steam irons.

So the cost really is no object here. Pick the most convenient provision. Don't buy deionized / distilled water in large cans thinking you are going to save money by buying in quantity (unless you need it for ironing, that is). The opened flask of distilled water can develop a mould. The ideal would be to prepare you final bath with a new flask. You will reuse it for some time. Before using it visually check for solid deposits, mould etc.

Do install some filters on your tap so that you avoid putting some sand / solid particles in your baths.