first you've got to keep your ears open for particular people who want something yet are incapable of acquiring said thing themselves. Then you've got to provide these people with the things they want, in exchange for money. What you have to realize is that the harder it is to get something or the more someone wants something, the more money you'll get for it.
Now you said you want $800, this means you've either got to find one thing that'll be super hard to find, or something that someone wants reallllly badly ($800 badly). One example, sparkly rocks, are typically hard to find but fetch a pretty penny especially when you put them on a ring or a necklace, if you find a big enough one you probably could get $800. Else wise you might try to find something that people desire a whole lot. If you want to go this rout, try picking a particular demographic and apealing to their desires. For example, hungry people really want food. If you find a hungry person you could probably charge them $800 for a sandwich, if they were hungry enough.
you'll probably run into some problems (viz. hungry people are poor and could never afford an $800 sammy, or sparkly rocks are impossible to find unless you're a slave in an african dimond mine -- in which case you wouldn't even have access to the internet, lol.), but that only means you've got to figure out other things you can do, that others want done, but aren't willing to do themselevs. It's called a JOB, just get one.
In New York they wants me_And I'm gonna be there_Van-city's calling
And I'm gonna be there_In T-Dot, they wants me_And I'm gonna be there, spreading the vibes_All over the world