rebuilds cost 1000 - 2000 because there a four stroke but 2 strokes are only like 1 grand but you do not have to do them as often if its a four stroke. if ya like doin motocross aswell id go the 150 because of the 230 forks. although be aware that the 150 is a midsize - 3 quarter bike meant for kids around the ages anywhere from 9- 15.
in my opinion i would go for a like 00 01 or 02 model cr125 which would be around the same price.
tip: If ya keep the top end nice and fresh i.e changing the piston and rings every 12 months and keeping fresh engine oil in there it will extend the age of your engine.