Hi. The most expensive part is getting the proper set up. I have a roach colony and grow my own greens. Winter all I buy is greens. So maybe 5.00 a month.
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!!!!
Ya beardies are not cheap unfortunatly in my experience. We just started up our dubia colony and still have months before it's of any use to us so we must buy food which usually costs us about 30 -50 a week between the 3 dragons we currently have. I believe the set up costs have been covered pretty well here.
I will add, vet bills can add up quickly. One of our guys is sick and it has cost us quite a bit. If it wasn't for our vet being so good to us we wouldn't know what to do. They did a scope for 100 dollers and are giving him an ultrasound for free, without this it would have costs about 1200 here in Canada, not to mention the 3 x-rays they have given him. The cheapest part is medication which tends to be very reasonable. We have been blessed with a vet who loves reptiles and wants to learn more about them so it has really benefited us.
I wouldn't say this is normal, but I'm just throwing it out there, it can be expensive especially with the poor breeding practices and genetic manipulation done to get all the varients you see these days.