I would personally dump-mould and cold-cast it from a Monster Clay master, but air-dry clay would be your best bet if you don't have oil clay and casting materials. Bondo's tricky to use and trickier to sculpt with, especially on something detailed like that. If you have a friend who's talented in art class, they might be able to get it pretty close with regular clay.
Then obviously spray it silver. The best silver spray is Design Master Premium Metals Super Silver, but it's $8 a can and only available from Michaels. The Rustoleum Universal silver spray is ok if it's never going to appear close-up on camera. If you know someone with an airbrush setup or an auto body shop, you might be able to use a metallizer laquer, which is the best metallic finish but kind of expensive and hard to use.