I don't know, but....
Your overhead is very low as a young enlisted type. You get housing, fed, and some uniform allowances. So, you mostly have to pay for personal care (hygiene, haircuts), and transportation.
My advice to anyone joining the military: Live in your barracks. Buy a bicycle. Put away $300 or more a month off the top into a Mutual fund or at a minimum an ING savings account. When you have enough money saved, buy a car outright. Do not get an AAFES credit card. Get one credit card for $500 or less, and buy yourself dinner on it once a month, and then pay that off. Take advantage of the free movies on base, base transportation into town, and any other free or cheap activities you can do. Until you're around an E4, you're just going to be broke.
If you get deployed, save any differentials right off the top. Put that away somewhere deep, like a Mutual fund.
DO NOT INVEST IN SAVINGS BONDS. They will pressure you to do so. Its a ripoff. You don't make squat on them. Instead, setup a Mutual fund that will allow you to invest via allotment.
If TSP is available to you, invest at least the matching amount (TSP is the federal 401K), which I think is 5%. Go agressive, which is the S and I funds. If you take out a loan against it, I will hunt you down and give you a swift kick in the nuts.
I made alot of these mistakes when I was young, and left the Marines after 5 years with almost $30,000 in debt. It took me 4 years and a job at over $100k a year to pay that off finally.
Are you locked into the Army? Check the other services out! See what jobs you can get, especially any that involve enlistment bonuses!!!!!
Good luck,