Where does the money i am receiving come from? Say i was to have 100,000 dollars worth of bitcoin in my wallet and i want to cash out, where does the money i am receiving come from? Is it taken out of the volume amount of dollars currently in circulation or can you only get paid out if someone is willing to buy it?
You would need to find someone to buy the bitcoins from you. Simple as that!

You can do this in person (probably with someone you trust if its $100k!), or through an online exchange (a service that matches up buyers and sellers).