Prague is still relatively inexpensive in comparison to other European destinations. A rough estimate would be to bring along an extra $1200 to $1600 for spending money.
You do not want to bring travelers checks, they are a pain and no one uses them anymore and they are really hard to cash in Prague. Bring an ATM card and withdraw money as you need it. That is the best way because you get that days exchange rate and you can withdraw a bit of cash every few days so you do not have large amounts of money lying around, that is what we do and it is the safest and most reliable way. If you are worried, you can bring $200 in cash to get you started which you will exchange at the airport when you arrive. Your driver will be at the airport and you can ask him/her where the exchange center is, it is right there in the terminal, along with a line of ATM machines. Your airport pick up is paid by us, you do not pay them unless you wish to tip the driver. Our staff will be waiting for you at the res hall. I would for sure not bother exchanging cash at your bank before you come to Prague, they will charge you a small fortune and it is not necessary. You should wait until you arrive and do it at the airport, either exchange Dollars or pull money out from your ATM card. After that, just use ATM machines, that is what we do and the machines are located everywhere. While some places will accept Euros in Prague and in Czech Republic, you will get a far worse exchange rate than using Crowns. Also, credit cards are readily accepted throughout Prague. You may have a small international fee attached to your credit card service but it is handy to have available if needed. I have no experience with the pre-loaded cards and I have never heard of anyone ever using them. Just go the ATM route and credit cards are widely accepted.