iroc stangs

hi well i want to start modding my 87 iroc 305tpi/auto and get some good power before i start driving ( im 13 ) and well my whole family has limited amount of money but im trying to start saving up ( 15 bucks a big stack of money dont ya think lol jk ) but i will only be able to get limited stuff when buying new so i figure i might as well try to find good condtion used parts and the first thing i need is a new muffler and i was thinking of flowmaster 80 series i liked the sound of them from what iv heard. i like a deep muscle rumble that is a bit louder then stock but not annoying. how much do these run used? can someone find me 1 of these mufflers used for cheap plz? i need 1 soon before the car really gets messed up. but other then the muffler problem the car runs perfect. is there any other suggested easy to replace, cheap, used parts that i should install? i need intake runners because mine are dented severly. plz give tell me what parts you suggest that are cheap and used and plz give me the link to them thx everyone.