> I've lost a decent amount of money to inflation and opportunity cost.

You also obviously know that one ride on the S&P 500 from a relatively low point, will bury such inflationary losses in dramatic fashion. And one bad ride down from these heights could easily cost you the better part of a decade to fully recover. First do no harm, don't lose money; don't chase or try to force returns. Patience plus money is the critical combination to being positioned to pounce on opportunity. Most people lack the cash when the opportunties are plentiful (eg 2009-2010). And you don't need very many big broad hits (like riding the S&P to a triple over six years out of the great recession) across a lifetime, only a few.

> I know there are better things I could do with the cash in the meantime

This deep into an expansion (10 years at that), I'd say that now is exactly the time to hold the line on your patience. The stock market is seeing close to flat earnings growth and its multiple is very high, combined with everything else it certainly appears to be an out-of-gas scenario. We would need to see rather extraordinary earnings growth - and soon - to buffer the earnings multiple this market is carrying. And we're also not seeing macro economic growth like you would want to see, to feel confident in the market moving much higher than it already is. In the late 1990s we were seeing 4-5% growth (18 straight quarters of 4%+ growth in the late 1990s), now 2% is more common. China was an engine for the world economy for ~15 years; that is now over. Where's the next engine? There may not be one in the near future.

A large share of this market climb the last few years has been nothing more than multiple expansion, it's not coming from an organic surge of earnings growth and productivity growth (the tax cuts were a big part of it, which wasn't organic; that adjustment spike is over). I consider this a very dangerous market based on growth rates & multiples (Warren Buffett appears to also hold that belief, based on his net equity selling and refusal to deploy Berkshire's epic $122b in cash; few have consistently navigated such circumstances better than Buffett, whether 1999-2000 or 2007-2008, he has a rigid wiring for it based on the value available to be purchased with capital; his spidey sense is tingling, clearly).

I'd suggest you stick to being patient, wait for a better price vs value environment, and or for another major financial opportunity that comes along in your personal life. Lacking the capital to seize on opportunities when they become abundant, is a truly terrible trap to be stuck in, infinitely worse than the modest inflationary mouse nibbling at your capital now.

Others will note something about not timing the market. Keep in mind this is absolutely not about timing a market. It's about being unwilling to dramatically overpay for what you're buying (eg paying a 30x multiple for zero growth on various blue chips). It's calculating value for price. That is not a matter of timing, it's a matter of deciding what price you're willing to pay for what value you get. Buffett for example isn't a market timer (he points this out at every opportunity, going back many decades); rather, he has fairly strict rules about what he's willing to pay for what value he gets. Being unwilling to overpay is not about timing or guessing, it's about having rules for what you're willing to pay for what you get.