It's time to place SPY/SPX longs here, you don't really need a stop loss if it's part of your investment portfolio. You could establish a hedge by buying IBB puts at $255, Dec 16 expiration, but it might not be needed after the smoke clears out.
Risk is basically a new daily low, but you could go with a wider stop as well, or none at all and simply size it as a % of your account that fits your risk profile. If going with an investment type position, you would use part of your cash, for a non-leveraged SPY long position, I'd reccomend 10% at least, and you could buy puts at the money in SPY, or IBB, which you can sell for a minor loss once we're confident the bottom's in.
Or, you can spend half the cash on SDS longs as well, which would hedge the position with half the cash use.
The level we tested here, the speed line support, the VIX retracement BIG$ support, and the sheer panic makes this a possible candidate for a long term bottom in SPX, so don't miss the opportunity. Or, you can believe the boys screaming wolf again...
Good luck,
Ivan Labrie.