I'm an avid DIYer and an overall cheap bastard. But, I have ramped up and acquired toys over time. I'm now electric with a 3800 watt induction burner and that's a longer term investment to save over propane (though I did catch a sweet deal on that too), 3 tap kegerator, and more crap than I know what to do with. But, almost all of it was acquired used or DIY'd. 'Cause, cheap bastard...
Starting out, a lot can be saved by watching Craigslist, garage sales, and diy-ing simple things like a copper immersion chiller. As mentioned, there's always someone getting out of the hobby or upgrading and clearing out their old stuff. Keep your eyes open for bargains and think about where you hope to go in the hobby, so as to minimize buying things you outgrow (I failed badly at that part). I started with BIAB in a repurposed turkey fryer I got off Craigslist for 30 bucks, a 15 dollar rolling cooler for mashing, a glass carboy I nabbed for $5 at a garage sale, rescued beer bottles, and not a ton more.
Saving/culturing yeast and growing my own hops are big time money savers for me these days, but they do take a bit more time and equipment. I caught a deal on a stir plate, but you can diy one pretty easily too.
But, it all comes down to what you want out of the hobby. Personally, time isn't as much the issue for me and I get as much satisfaction making my own equipment and growing/culturing my own hops and yeast as I do brewing. If you only enjoy the brewing and consumption part, then watch for those sales and listings for used equipment and screw the diy part. You do you. There's no right or wrong way.
If you're trying to save ingredient cost, find a good supplier, go bulk, catch sales (but don't overbuy things with limited shelf life), and find recipes or beer styles you enjoy that rely less on specialty grains and use less (or less expensive) hops.
Your water expenditures sound crazy to me. Before I diy'd the immersion chiller, I was cooling my kettle by gently swirling it around a bathtub of cold water. And, I live in an area where our water is good for brewing with minor adjustments. Get yourself a water report if you live in an area with municipal water. Carbon filter and some inexpensive adjustments are a lot cheaper than investing in a RO unit or buying bottled. But, a decent RO unit isn't too bad and will probably save you over time. Do the math and figure out the costs over time once you account for the cartridges.