Things you will need
1. Metal net or woods.
2. pieces of hard wire.
However make a rectangular shape cage with one side open to fix a door. Height x width x length of the cage is up-to you, estimate a relevant ratio according to the targeted animal.
For Asian Cats i used height= 8 inch, width= 8 inch and length= 15 inch.
It cost $0 for me because i used the materials which i could get from home around. but if you need to do a fresh one may be it will cost about $10.
Step 1: Door
Step 2: Bait Holder
Step 3: Trigger
Optional: Make sure the door is fully opened by keeping a small wood block between the cage and trigger wire. but it should not make hard to pull the bait hook.