The S&P 500 just tracks the largest 500 publicly traded companies. So no, it's not difficult to approximate.
So at the £5ish/trade of my current broker, that's a cool £912500/year on just commission.
For some reason the massively reduced ease of entry to a trading strategy like this is never considered when lauding its historical performance.
Modern S&P500 funds like SPY or VOO rebalance quarterly FYI