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...).
Flax Substitution tips. 3 tbsp (45 mL) ground flax seed for each 1 tbsp (15 mL) of margarine, butter, or cooking oil (3 to 1) . This is especially for those who cook Gluten Free food! Substitute ground flax seed & water mixture for eggs in recipes such as pancakes, muffins, and cookies. Use 1 tbsp (15 mL) ground flax plus 3 tbsp (45 mL) water-left sitting for several minutes-for each egg. Note that this will result in a chewier version of the recipe with less volume.