How much money does someone have in Vanguard S&P 500 if they pay $20 / year from the expense ratio?
Would you believe $40,000? The expense ratio is 0.05%, and 0.0005 x $40,000 = $20.
If you start out investing $10,000 then Vanguard is only taking $5 of your money per year.
Back to your index fund, maybe you start with purchasing 50 stocks. Now tax time rolls around, and you have dozens of 1099-div forms, showing you dividends. You get to read each form, type it into your taxes, and figure out how much you owe. If your entries don't match what the IRS computers are seeing, you also raise your audit chances. The time you spend purchasing, tracking, and doing taxes... is that worth $5 per $10,000 invested? Meanwhile Vanguard Total Stock Market issues a single 1099-div for 3600+ stocks. Investing $72,000 you pay just 1 penny in expense ratio per stock ($36/year).
The idea of creating an index fund is interesting, but you stated the reason is to save money. But you need to weigh how much time it will take, and how much money you save. If your reason is solely saving money, it doesn't sound like a good idea. If you had another reason for doing it, maybe with a fraction of your investment money, maybe it's a different story.