If you refer to post http://organforum.com/forums/thread/114739.aspxyou'll understand why we all want to be more cautious about making sales quotations in the dark.
Please tell us more about the type of sale (dealer/private party) and if you've considered other instruments in your search or already know you definitely want a Conn.
It is also important to know if you are interested in the spinet because of space considerations where you will play it. Otherwise, a console has fuller sound and should retain a little higher value through the years.
It will be important for you to know if it has been played regularly and what type of maintenance it has been receiving. Best case scenario will be that it is not only cosmetically in good condition but has seen regular use. If that is so and you don't mind the possibility that anything could happen to the electronics at any time (for which a dealer may make some warranty) as the earlier mentioned thread will tell you the next big issue is location.
If in your area stock of used organs is low the price will be a little higher. If you live in an area where good used organs are easy to obtain, the price will be a little lower. All said and done my personal shopping budget for that model would range under $100.