If a company isn't even willing to pay you minimum wage (which is really not much in most places), it is one or more of:

1) They can't afford to, so probably aren't a very successful business.

2) They want to keep out the people who literally could not afford to live under this arrangement. (Disproportionately non-white, female, etc.).

3) You'll be of even less value to them than the minimum wage (so probably wouldn't be doing anything worthwhile/educational).

Don't take an unpaid internship, even if you can afford it. It perpetuates a terrible idea.