It will have something to do with you selling something that somebody else wants to buy (especially with delivery lead times for new machines).
The Raven 1 is still a good machine with the original Lycoming engine and a lot less to buy then the 2.
Also if the machine you are selling has something special (i.e. pop out floats or it's an IFR trainer).
That being said, there are a lot of R1 and R2 machines in UK&I now so demand and supply are more balanced than when the hydraulic machines came out in 2000.
Check out Helidata Classified for resale prices in UK&I.
http://www.helidata.rotor.com/
It's the non hydraulic machines that are absolutely in trouble in price terms now IMHO. It is possible to pick one up for less than the price of an R22 (and not a new one).
The real question is how any of the prices will change if Robinson move to a different engine type to address the AVGAS question over time. A diesel running J A1, now that would change the game.
Also, if Robinson were to focus much/ all of their production capability on the R44 at the expemse of the R22, then there would be an uptick in demand for Ravens for training schools, which may rebalance prices a bit.
No hard and fast rule, depands on age/ condition/ hours/ salesmanship of seller/ equipment on board/ colour (of machine)/ etc