There is a lot of cheapest coin you can buy on an exchange, but you don't know which coin will give you a profit. You can find them in every exchange, and you can start to buy, but I won't suggest you do that because that will be too risky. You should select some of the cheapest coins, especially for the coin who have a better position in the market. You can check it on the big exchange which coin have the cheapest price so you can buy the coin. But always research before you buy, so you know the right coin to hold.