[mothballed]

Shorts don't cost much to open, just the borrow rate on the shares. As long as it goes straight down you can leverage quite a bit without getting called.

Of course, this is the fastest way to lose your shirt and everything you have ever worked for, if there is any uncertainty.

[FireBeyond]

Yes, I'm sure Robinhood or Schwab will allow me to open a $2M short position when my portfolio is $[sufficiently small that I'm debating the costs of a couple of thousand for a helicopter charter].

[mothballed]

It's easy enough to synthesize 100x leverage by synthesis through options. If you have $25k for a margin account you could do it no problem. Of course, your funds would be rapidly vaporized if you were even a little bit wrong on timing or you needed more margin for volatility to keep it from getting called before it dips.