Niles? They are cheap. At the reptile swap near me you could get one for $20. If kept properly (i.e. feeding regularly, proper enclosure, enough heat, etc.), they can grow FAST too. I'd say expect 2-4' in the first year.
How long did it take your savannah to get that big? i've had mine about 10 months and he is about half that size. he was only about 7 inches when i got him. does that sound like pretty good growth for that time period?