Here is a great video from fellow Neil, Neil deGrasse Tyson.
For those who didn't watch the video, he states Bill Gates net worth is $50B. He makes a point that an average person like himself wouldn't probably pick up a penny (1c), a nickel (5c), possibly a dime (10c), but most likely a quarter (25c) would be most people's minimum. If you scale it up to Bill Gates' net worth, the equivalent would be $45,000. It's a nonsense equation but quite entertaining.
No idea, if it's of high value I'll try to find the person who lost it and if not possible I'll give it to a worthy charity, or a struggling person. I won't keep it or spend it because in my book that is wrong. I'd hate to be a person I don't like.