Id estimate the earliest intel models to be worth around £400 assuming it all works and is reasonably clean/undented for its age. the G4 machines now are pretty much worthless.
The problem with your price, is (perceptively) a new macbook air costs £850 and a new macbook pro costs £1000 - we all know thats not really the case, as its just apples marketing of the lowest spec of each range, which your laptop isn't.
I think your price expectations are realistic, but offputting to casual browsers or impulse buyers. I'd go for ebay but with a long auction run time, and take time over the photos and description. If you just need to get rid of the thing quickly to raise cash then you could sell to a shop, but you'll need to accept a lower price. Someone who actually knows what the computer is and what they are worth should come along eventually.
I know its a bit naughty, but if it happened to still have photoshop, or logic or similar nice software left installed on the hard drive it would make it more attractive to the second hand crowd.