Here is the simplest way to build one.
1) take a rubber made tube with a lid.
2) cut a 2" dia hole in the bottom at one of the corners.
3) prop up one end of the tub (the end with the hole)
4) Prop it up at a 35 degree angle (angle is important)
5) Put a can or bucket under the hole
6) Put the lid on, but prop up one end 3/4"
Here is how it works. You put your waste in the bottom.
The Black Soldier Flies will fly in through the 3/4" gap and lay eggs in the food waste.
When the larve mature, they crawl away looking for a dry place to pupate.
They can crawl up to a hudred feet, they will climb up and all around annd eventually find the hole and fall in the can.
That is all there is to it and I just saved you same major bucks.