You'll need a cosigner, absolutely without a doubt to finance anything over about $1000.00 with no credit history. If you can get a parent/grandparent to cosign, look for a nice used Kawi 650 Ninja or a Suzuki SV650. You will outgrow a 250 ninja in a day, and if you get a ZX6R the bank/finance company will require you to get full coverage insurance, and you insurance payment will be more (probably much more) than your bike payment, for good reason. They know that within a year they will be paying for a titanium rod, plates, screws and about 3 square feet of skin grafts.
Your gonna hear this alot in the coming posts from other experienced riders, but its very, very true. Get a used, SV650, EX500, GS500e or f, 650 Ninja. These bikes are very reliable, nice, mild mannered, all are capable of speeds that will get you arrested but are much less likely to let your learning rides become deadly. The 650 ninja and the SV650 are both very, very good bikes, plenty fast, and insurance payments will be less than the bike payment. Good luck.