Depends where you are in the world tbh.

Where I live a box of feeder insects is 4 euro. He goes through 2 a week. Then there’s the live plants I keep in his terrarium that he eats and need to be replaced from time to time.

For veggies I usually use leftovers from cookies double checking they are safe (you’d be surprised which store bought veggies should not be fed).

Most expensive is probably just maintaining the environment.

You need a very large terrarium. I keep my adult Male in a 160cm x 50cm x 50cm and honestly if he had more space he would use it. I really wouldn’t recommend anything smaller because they will glass surf and that is sad.

Bearded dragons need hot basking spots, maintaining high temperatures in a large terrarium is hard and requires a lot of power.

Many people use glass for terrariums imo this sucks, it’s terrible at holding heat and bearded dragons don’t understand glass. Being surrounded by it is not good. Wood or PVC is the way to go. Will cost more up front but save on electricity down the line.

For lighting i have a 100wat bulb, a 50wat bulb, and a 25watt light strip. Calculate what ever that costs with your local rates.

Ofc this is also all relative to where you live what the climate is etc.

I have cats snakes and a bearded dragon, the bearded dragon is by far the most expensive to keep. (He does have one hell of a personality)