yea a ninja 250 is a good start for a first timer, but most people grow out it it really quickly, as did I.

If you are not comfortable riding yet, get a 500 or a v twin 650. those are great bikes to start out on also.
if you are set on a 750, there is one for sale on georgiasportbike.com it is a 89 katana 750 for 1500 OBO. great beater to learn on and now worry about dropping.