They have gone up steadily over the last 5 years. Well, I guess anything good has, but they were overlooked in favor of the #0#0 series and G series.
I would offer $150 and go from there. Wheeler-dealers always want the other party to make an offer first. Better to be on the low side before the negotiations start.
If it's an item you have been lusting after than the numbers from the post above are not unreasonable. If not, stay close to your original offer.
I sold my 9090 a couple months ago. I was shocked at what they are fetching. Broken ones are selling for twice what good ones went for 5 years ago. I kept the Eight but a neighbor is using it in his main system now.