How much money does it cost to start doing bitcoin?

If you start with Bitcoin specifically, you will need such a large amount that it isn't even worth looking into.

Mining isn't even close to profitable anymore because of this, and I would recommend staying away from it unless you're banking on a particular alternate coin substantially increasing in value.

You can put a smaller amount into a different crypto and trade between coins and make a decent amount of money that way, but you need to keep a close eye on the markets. It's essentially the same as day trading with the stock market but far more volatile and therefore has a significantly higher risk/reward involved.