Depending on what you make it from, I can only imagine at the very worst of it costing at around $50 to $60.
LED's, wiring, solder, resistor, batteries --> $20 to $30 relatively.
Wooded infrastructure --> $1 if you buy it out of the junk pile at home depot.
Outer shell --> $5 to $30. All depends on what you decide to make it from being foam which is cheaper or hard plastic which is more durable but expensive.
Now these costs are strictly for the megabuster alone.
When in doubt, just take the next small step.
With that next step take a deep breath. It calms the mind.
When the mind is calm you realize the best is still yet to come.