I agree, being more realistic (a roach colony takes months to establish and obviously growing your own greens isn't always possible for a lot of people), you'll pay between $300-$500 for the initial setup. You're better off buying the adult size enclosure when you first get the baby beardie so you're not buying multiple enclosures. So a minimum size enclosure is 4'x2'x2'. Then you need an adequate 18" or 24" 10.0 UVB Tube light, and a matching flourescent tube light fixture. Then a basking bulb and matching deep dome fixture or clamp lamp. Then you need at least 1 or 2 digital probe thermometers. Then whatever decor you want like hides, basking platforms, bowls, a solid substrate, etc.
As far as monthly costs, obviously your main costs are live feeder insects and greens/veggies. If you order your live feeder insects online in bulk you'll save a fortune, especially if you choose crickets, dubia roaches, or BSFL/Phoenix Worms. I spend probably $15-$20 a week on food per dragon. Realize that from a baby to a year and a half old they are eating 90%+ live feeder insects, then after the year and a half to two year they will start eating mostly greens, so you'll spend much less. You'll also need to periodically buy basking bulb replacements, and every 6 months to a year you absolutely must buy a UVB tube replacement. You'll also periodically need to buy Calcium and multivitamin powders.
Please, please, please budget putting money away for vet care monthly as well. This is just as important as buying anything else. It's the items like sudden necessary vet care,
UVB light replacements, basking bulb replacements, Calcium and multivitamin powders, home medical supplies and supplements, etc. that NO ONE EVER BUDGETS FOR!!!!