[travis]

Pb? HAH! Only the bumpkinest of rubes go to Plumbum (specific gravity=11) for density -- it's just half that of the high end stuff and has dismal physical properties.

It is some kind of cruel joke that Earth didn't get more Pt. Even with the high density (SG=21), if it were more abundant they would probably make turbine compressor vanes out of it. You can boil Pt under pure oxygen and it will never react, all with better strength than Ti (pffft SG=5). Best of all, your friendly inspector could file it into powder and make a healthful beverage from it. Several rappers and I even have teeth made from the stuff. You can have about 2.5 Oz and still be under the cost limit.

Someone out there sells depleted U (SG=19) counterweights for the aircraft industry and unitednuclear.com gets a hunk now and then. Non radioactive U is still chemically poisonous though. The IAEC will send inspectors to your school should you amass more than 15 lbs of it.

I spent months tracking down a guy in Sweden to sell me a used Ta (SG=17) sputtering target to make my wedding ring from. Polished Ta is like looking into the cosmos; there is nothing like it. A W/Re (SG~=20) alloy ended up on my finger for various reasons, but I will trade a size 9 Ta ring for a Haas tool room milling machine with full software upgrades and will throw in the Ta remnants for a 6" Kurt vise.

As so often is the case, none of the really cool stuff is a viable option, but you are in luck. Your local expensive outdoor store should have W (SG=19), both in the form of fishing weights and bird shot, for about 10X what they charge for Pb. Forget about the inspectors, call a tooling manufacturer if you figure out how to machine W in the pits. There have been more studies linking Al (SG=a paltry 3) to heath problems than W, so you could leave it uncoated and in the open.