In order to collect rental income, you will need to purchase real estate or own real estate.  This would involve putting a down payment and then borrowing a home loan or mortgage (or if you have it all in cash, by all means!).  If real estate prices go down and you sell, you will lose money.  If real estate prices go up and you sell after collecting rent for a year, you will do well.  Just like the stock market, the real estate market is cyclical and there is inherent risk in investing in real estate.

You don’t have to invest individually to take advantage of dividend paying stocks (i.e. investing in an ETF like DVY, which currently has a 3.16% dividend yield – almost 4%). And while your math is indeed correct, there is more to dividend paying stocks that just the math. The reason the companies pay dividends is typically because of their underlying strength, steady growth, etc. These companies can be good investments for the long run. As such, it might not make sense to sell.
Acorns: Acorns is a great way to start investing and building wealth. As it turns out, Acorns will pay you $5 to start investing with them for as little as $1. That’s a 500% return, plus it’s probably time you started investing for your future. They even have features like round-up and found money that allows you to get free money from places you already shop at.
This was my first foray into passive income.  Putting your money in a high-interest savings account is a great idea because it is safe and usually these are e-savings accounts so that they are a bit more difficult to access (e.g. you won’t be able to raid the ATM and withdraw all your savings to buy that pair of shoes you have been eyeing).  Which means that you’ll have less opportunity to meddle with your money, which means the money will be left untouched and left to grow with compound interest.
I used to be wary of Ebates (now called Rakuten) because I thought the cashback didn’t amount to much, but now I love it.  I’m converted!  To earn money through, all you have to do is sign in and then look for your online retailer and shop through the portal.  Then you get cash back in a few days (it says on the website).

How much money do you need to make passive income?