How much money does it cost to start doing bitcoin?

Well there are 3 options:
a. Purchase hardware and start mining Crypto
b. Buy Crypto, hold it and hope that the price will go up someday
c. Trade Crypto like Forex -> buy cheap sell expensive

Now:
a. Don't recommend it. There are already waaaay too many people doing this. There are companies with huge mining centers and they are barely making any profit. If you purchase some GPUs and try to make some profit, it will take too many years.
b. That's a bit more worth it. You don't need thousands of dollars, but if you invest more money at once, the profit can be bigger. Wait for BTC or any other important Crypto to go down a bit or to crash, buy when it's cheap and hope that it will go up someday so that you can make a profit. It can take weeks, months, years or it can never recover.
c. You'll have too have knowledge in the trading field, because you can loose a lot of money very very fast. Trading, in theory, it's easy: Buy Crypto now, sell it in 5 minutes, 20 minutes, 1 hour, etc. for a profit.