Cheapest Tungsten on Ebay, You get 8 Cylinders for $14.60, not 4 or 2 oz

3/8" Diameter Pinewood derby car Weights - Tungsten Cylinders x .400" Length 8 Pcs

Total Weight 3.7 to 4.0 Oz,

Tungsten is about 1.7 times heavier than lead and 3.2 times heavier than the no-lead weight often used on pinewood derby cars.

It is non toxic.  Use a standard 3/8" drill bit and wood putty. 

95% Tungsten

3.5% Nickel

1.5% Iron

Each Piece weighs .463-.500 oz, lot size  of 8 pcs weight is 3.7-4.0 oz