For my zip code the average NADA retail value for a 2007 Kawasaki 650R is $4,150. You then subtract for the repairs needed and a dealer's profit.
The 250cc Ninja or a dirt bike are better for learning, but the 650cc twin is a lot safer than a 600cc 4-cylinder for a beginner, especially if you are extra careful with the throttle.
I would have a mechanic check it over and test ride it before making a decision. Take the 3-day Motorcycle Safety Foundation beginner course as part of getting your motorcycle license, and budget for a helmet and protective clothing.
The average motorcycle is ridden maybe 3 to 5,000 miles a year, compared to 10 to 15,000 miles a year for a car, and if they changed the engine oil on a normal schedule (at least once a year) then 11,000 miles on it is not a big concern. Ask them if they used synthetic oil after the first 600 miles.
"We have created a Star Wars civilization, with Stone Age emotions, medieval institutions, and godlike technology. We thrash about. We are terribly confused by the mere fact of our existence, and a danger to ourselves and to the rest of life.”
― from Edward O. Wilson, The Social Conquest of Earth.