The good way of doing business for $ 500 is buying things online for cheap when there is huge sell, then selling it off in Craig's list or ebay or amazon.
I've sold lots of stuffs like that, from printers, cellphones, gps, to Windows vista disc, and many many more, in most of the transaction I made 100 percent profit. Ebay and amazon charges like 10 - 15 percent commission, so craig's list is a good place to put your ad.
however you do need patience and also you can't really depend on this as your primary source of income, this is just as a side job kinda thing.