Are you willing to pay someone at least $2500+ in order to build your credit? If you are then do it.
If you end up getting the bike for $5000, the current trade in price for a 2011 cbr250r in good condition is $2,480.
http://www.kbb.com/motorcycle/trade-...br250r/361773/ This number will not get better in your favor as time goes by.
If you didn't know, a credit score is nothing more than a "I love credit debt" rating. Open a couple of new credit card accounts and run up some debt, don't have any late payments and you will grow that credit score. Just keep in mind that its really easy to get yourself in financial trouble doing this.
Good luck with it.