you are better off buying a bandy spanken new Banshee Bungee. used ones are unpredictable because they only have a life span of about a year, two tops, before they snap off in your face. which blows.
bike tubes sound like a good idea but you might want to look into something like surgical tubing. i know it sounds weird but its super stretchy and i think its pretty cheap. Good luck bro and if you find anything that works really well, pm me!
i have no idea how the home depot stuff would work but anyways my local shop sells the banchee bungee, or something like that but i think its pretty expensive
Dude you guys are being cheap, just go out and buy a Banshee Bungee. They are reliable, durable, work and are a lot of fun. Your gonna end up blinding and/or hurting yourselves by making your own.