That 8K should come close to buying a new one. Problem you find when pricing one is the amount sounds fine until they start adding shipping, installation and taxes to the price. I think with all added up, it should come to just over 8K. That could also be at 0% financing. I spent around 7.5K to have my BH75 installed on my L2800, at 0% and I don't believe the BH90 is very much more.
I think I paid about $7k installed back in January, but that was also part of a complete tractor purchase. $8k seems pretty steep for a used one though.
I paid 9100.00 installed for a BH90X Woods hoe with a hydraulic thumb. The thumb and hydraulics for it were @ 2k so i would say that 8k is pretty steep for a used one if it has no thumb. Although I did purchase mine with the tractor as well.