Platinum tends to be worth more than gold by weight, but as prices  fluctuate, sometimes the gold price does go higher than the  platinum price.
To substitute for 1 egg you can use ingredients you already have. 1 Egg = 2 tbsp. flour 1/2 tbsp. butter 1/2 tsp. baking powder 2 tsp. water. Two years ago my daughter (who was 9) did a science project about this very subject. Basically, the eggs were binders to keep the cake together (and they did add flavor...).
1 Just follow the directions on the box-this replacer is a baking substitute only, though. 2  Flax seed can be used as a substitute for eggs. 3  Grind 3 teaspoons flax seeds in a coffee grinder and whisk into boiling water. 4  Leave it to stand for 5 minutes before adding to your cake mixture.