Those were great machines in their day; we sold a lot of them and many of our customers are still using them; we have a few with over 20,000 hours on the engines.
When you are trying to establish the value of a used machine, here's some things to ask:
What does the comparable
Prochem machine sell for new? Since that model is no longer made, your closest comparison would be a Prochem
Everest. That machine is around 24K right now.
Are you buying is "as is", or with a warranty? Some distributors refurbish these units and warrant the machines for a few to several months. Such a warranty adds value.
What other accessories and tools are available with it? Does the price include installation and a fuel kit? If you are putting this unit in a new van, the fuel kit alone could cost several hundred dollars.
Check some of the on line sites for used equipment, such as:
www.cleanersclassifieds.com and sites such as truckmountdeals.com and the Jon-Don used equipment site to get comparative pricing.
The advantage you have with this unit being at your local dealer is that you can run the unit and discuss its condition and possible warranties and perhaps financing.