Whatever you can get a heck of a lot of for under 15 dollars?Depends in part on why you want to make it. Just for fun and to practice your chain weaving? To have it look good? To have it look _convincing_ to someone who knows what they're looking at? Do you care how heavy it is? (Serious mail weighs quite a bit; if you want it for LARPing you may want to cheat and use aluminum.) Websearch on "sca chainmail" finds several makers and articles (one good starting point: http://lochac.sca.org/lochac/artsci/articles/chainmail.html),. Some of the makers say what they're using (one says 16-gauge galvanized steel, for example). Those may also give you some indication of just how many feet of the stuff you'll need, which will interact with your budget.There are several articles here on Instructables about making mail (or maille; both spellings are accepted). You should probably glance at what they've used.Of course there's always the joke approach: a shirt made out of chain letters. ("Make five copies of this shirt and send it to five other people...").