what is going to be the cheapest cryptocurrency to invest at present and get double future return from it? 
There are many tokens or cryptos to choose from that are having a market value of below 1usd particularly those that are from ICO projects. The problem that an investor would face on investing to such tokens is that, not all would have a price increase of 200% making your profit big. Mostly, market value below 1usd are not increasing that much.