This goal would be pretty easy to achieve for someone with $100k of spare money. It would be enough to invest in top 10 cryptos on coinmarketcap and although some of them may go down there always will be one or two which will not only cover that, but will generate an overall profit. But if you have only from $1k to $5k it's almost impossible to earn $1k/month, and if this is the case I advise you to lower your goal because with small amount of money the only way to achieve $1k/month is investing in risky projects, and although you may get away with it once or twice, eventually you will end up with nothing most likely.