Residual prior to first rebuild is higher than prior to the second because a tailboom is required, so rebuild costs are higher.
Also seems to depend on the general market: sub-600 hour aircraft depend more on condition, prior use and specification and can be quite aircraft-specific in a good market, but when things are slow all the sellers get hit!
Until recently, Raven 1 prices were very strong because low hour models were quite hard to come by.
BW