In a few weeks I'll travel from Europe to USA. I'll stay there for some months and in my fisrt period there I'll need a large ammount of money for living there (let's say 2000-3000$). So my question is: which one is the best way (trade-off between cheapness and security) to have money there? (Assuming that I'll open an account as soon I'll arrive there.)
What's quite relevant here is where you are coming from, not just where you are going to. Depending on your home country, many options won't even be available to you. I'll just go out on a limb, though, and say that you're from Europe, possibly Italy, and there you won't face many restrictions.
In short, bringing cash is probably the least economic option as you will have to exchange your currency (Euro) at an unfavorable rate, not to speak of the risk to carry such large amounts.
A transfer to your own bank account in the US seems like the best option. Though I'm not sure how quickly you can set this up.
In the meantime, ask your home bank to issue you a debit card you can use in the US. That gives you the best price and safety for your money withdrawals.
Last but not least, if the acc opening will take longer in the US, you could ask your home bank to open a USD account for you, convert Euros and connect a credit card to it. This way you could use the credit card in the US without paying high conversion fees. Just keep using the debit card to get cash.
Only you know what your bank at home charges for international wire transfers, so you will have to judge if it is fair value versus the risk of walking around with $3000 "on your person".
Many US banks have service fees for inbound wires as well, though these tend to be in the $10-20 per incoming wire. So a factor, but not a huge one.
Accessing your cash via ATM withdrawals is possible but can get spendy, as most machines limit you to 20 notes and many stock only $20 bills (though some may have $50) and of course they charge you each time $3 to $5
