bidding on ebay for mp-04....

i'm now currently bidding on mp-04 as low as 90 bucks US. my current bid is 31 bucks. however i never bid anyway on ebay, i just hope the low price that i bid for will pay off. can someone please tell me how ebay works? cuz i'm trying to buy the thing as low as possible, otherwise i would just go and buy the thing for 300 bucks in person.