After much searching I stumbled upon a reference to chalk powder used on gum paste flowers. Voila! That was the solution I was looking for. So here are the instructions to make your own cheap petal dust using chalk.
Supplies needed: paper, cornstarch, non-toxic chalk, tea ball, small containers, gloves. I bought a box of sidewalk chalk with 20 colors for $2.20, cornstarch for $2.00, a tea ball for $2.00, and a $5.00 case with 24 small containers meant for beads. So $11.20, which is about the cost of two 1/2 ounce containers of petal dust.
1. Disassemble tea ball into two halves, wash all containers and dry completely.
2. Put on gloves to protect your hands, grate chalk through tea strainer onto a piece of paper.
3. Add 1/2 tsp cornstarch, also sifted through tea ball half. The cornstarch keeps the powder from clumping, but it also lightens the color.
4. Mix together with your finger and pour through tea ball half one more time to combine.
5. Fold paper and pour powder into container. Use a paper funnel and poking device (I used a mangled paper clip) to help if the opening to your container is small.
6. Snap on the cap and repeat for all desired colors. After all is said and done you have an entire kit of powders, and a lot of chalk and cornstarch left over for several more batches as you need them.
I will caution you that although the chalk is non-toxic it's not really tasty. Since you will probably use it sparingly it shouldn't cause a problem, just keep in mind if you are covering large areas. You can mix the powders with clear alcohol or an alcohol based extract (like almond or lemon extract) and use it as a paint. The alcohol evaporates, leaving behind just the liquid color, this keeps gum paste and fondant decorations from becoming soft after painting. You can also mix with clear piping gel to tint for writing, although I recommend using gel or paste icing color for large amounts.
I hope to make some gum paste flowers soon and use my new powders. I'll post pictures!
Have a sweet day!