Less than 1% is possible on a reputable exchange.

It's entirely possible to put $1,000 in, end up with $995 of bitcoin, sell when that doubles to $1,990 and get out $1,980.

Then you have tax :)

I am in Australia but I am able to sell for less than 1% quite easy. I think it's easier for Americans.

Also you shouldn't have to worry about slippage with bitcoin unless you're selling $1,000,000+ in one go.

If you observe the order book orders put in at limit around a volume of $100,000 will fill at the limit within minutes or on lower volume exchanges like the ones in Australia you'll be filled at the limit within a few hours at that size.