So there are a lot of things to say in response to your post. First, you sound like you dont know enough about anything in real estate to know what you want much less what you should do. You should do more studying, networking, and research.
To guage what the market rate for a property is in your market look at recent sales of comparable properties such as by contacting a real estate agent and ask for sales comps or do it urself by looking at recent sales on redfin. Its really not that difficult.
Next, u dont need any money to be a real estate investor, but having some provides easier and more opportunities and avenues. For example, Its more easy to fund a $1m project if you had $1m in cash but if you had $0 and you had experience, sales ability, risk taking friends and family, etc you could raise a pool of money to fund the project possibly. So in response to your question about if 20k is enough, yes. you can do anything you want, in rei and in life. Steve jobs didnt have 20k when he started apple, i know its a bit extreme but you get my point, dont discount yourself, 20k is a good enuf chunk of change to do something. The question is what is that something.
Also note that while people make real estate investing to be super complex, buying a property and renting it out is really simple.
Within the realm of usual and more likely to do with 20k, depending on the price range of your market you could househack and get a 2-4 unit and live in one of the rooms. Managing that will teach you landlording, contracts, tenants etc. just make sure to look at the numbers, while it would be nice to cash flow it can be hard to do so if ur living in one of the units. So as long as your monthly loss is less than what you would pay for rent somewhere else you are effectively making money equal to the difference between the loss and the rent you would pay elsewhere. that doesnt even count equity paydowns and tax benefits of interest deduction.