Dont know what country you are in but you can change my filter
Here is some history for sales on the c30
Used Mcintosh C30 for sale on 300+ second hand hifi sites & shops. Use Hifi Shark to monitor pricing and global availability
www.hifishark.com
and for the MC2205
Used Mc2205 for sale on 300+ second hand hifi sites & shops. Use Hifi Shark to monitor pricing and global availability
www.hifishark.com
You will need to compare prices and condition and see what a reasonable price would be from the history.
Keep in mind the prices listed on hifishark are asking, they dont tell you the actual selling price (yes, it would likely be lower).
Additionally, consider if its a business or individual selling. It can make a difference.