Being Canadian, my price range going to be different but just convert the total cost into US dollars using any one of the many currency converters out there on the internet.
currently my dragon is about a year old (wow, the time sure has flown). I bought her at about three months of age. The first year is the most expensive year of dragon ownership as this is when they eat the most and move to their adult sized cage.
If you buy a baby dragon, you will need a 20 gal tank (mine I put in a 35 Gal tank at three months and moved her into her large 5'x2'x2' enclosure when she was about 6 months old). For the initial cage, light fixtures, hide, log, vitamines and calcium suppliments, I paid around $150. Then $60 for the dragon, so $210 Canadian to get my dragon and all I need to keep it happy. Crickets, I paid about $20 for 1000 crickets, adding in shipping and taxes. Course, had to spend about $15 to get a bin set up for the crickets.
Cricket costs for the first 5 or 6 months would be about $20 for crickets, plus about $6 on mixed greens. So for the first 5 months or so, you can feed your dragon for about $30 a month to be on teh safe side. Once they get older, they eat older crickets and more of them, and more greens. so the monthly cost will go up a bit, but in reality, not much more than $5 or $10.
However, since June of this year, I have switched to silkworms, which cost more but tend to last longer and have alot less hassle than crickets. So with silkworms and greens, plus silkworm chow (which tended to last a couple months so will spread the cost over those months) you are looking at about $60 a month.
Some notes here. For a single dragon, a bottle of repcal and a bottle of multivitamine, will last a year or pretty close to one. I haven't used up either bottle yet and I bought my dragon in March 2003, so not quite a full year has gone by of me owning the dragon. That said, my multivitamine bottle is still about a third full, and my calcium, probably around half. It is good to take a fecal to the vet at least once a year (twice would be ideal, and any time things don't seem right with your dragon). Fecals can range between $15 to $50 each, depending on the vet. (again this is in Canadian dollars).
To finish, bearded dragons don't have a really high upkeep cost per month, typically under $50 a month. However, it can be less or more, depending if your dragon gets sick, needs to be treated for parasites etc. then the cost could jump from $30 that month to $300, so it would be a good ideal to ensure you have free money for the unexpected expenses. If spending $30 a month is the Maximum you can afford, then better not to get a dragon till your income is more lucrative. Remember that dragons will be with you for at least 5 years, maybe longer.