How much money is taken from my initial pay check during BMT?

Initial clothing issue is on Uncle Sam's dime*, not yours. You will have to spring for basic hygeine and clothing maintenance gear, figure around a hundred bucks there, as well as a haircut every couple of weeks (about 2/3rds the price of a haircut on the street), Federal and State (your state of record, not where you attend training) income tax + Social Security. Most people find at the end of Basic they have more cash at one time then they will ever have again for a long time.

*A lot of people get confused by this point, and some services have a disbursement reg that makes this more confusing where on the one hand your LES gets credited with the book value of the uniforms issued and then gets deducted for the same book value. But all enlisted personel get their initial issue at no expense to the member, plus may get additional issues at certain career points (selection for recruiter or Basic Training instructor for example)

If I remember correctly, The EZ pay card for Marine Corps Boot Camp had 300 dollars on it. They don't take any money away from you it is just a reduced pay check for your first 3 months in the military.

You will be issued a debit card with $300 dollars on it, to be used during basic to buy supplies, pay for hair cuts, have your blues cleaned and pressed.

Uniforms are issued, you do not pay for them.