The bike is worth what you feel it is worth-for u to buy it.
If you want to buy it and ride it for a while then sell it, well then u have to go by the market price. If 5700 is what kbb is saying and the bike is truley that clean, then it is worth somewhere around that amount.
I would say 5k for an 03 in mint condition is what a bank would say it is worth. 4 to 5k for a well used 03 cbr600rr is fair if there is no horrible damage to it.
Really tho, it is worth what ever you feel you can spend on it. You are the MARKET, the consumer, you decide what it is worth. IF it is worth more someone else will grab it, if not, then watch it sit around for 6 months and see what you can get it for then. Look at the biks here for sale, some go fast (sell fast) some don't.
If you want an actuall value, you need to go to a bank and find out what they will lend on it. Othere than that u decide what it is worth to u. I love my 03 cbr600rr and I know what is worth to me, no one will pay me that amount and I know it.-EZ