Price depends on condition. Fire department trucks can be gems or junk depending on how they were taken care of and if they were heavily modified (hacked to pieces).
If it is a good runner and in fairly original shape I'd say it's worth at least three grand. I'd lowball them since you can always go up. Bear in mind it prob spent a lot of time sitting which can cause a lot of problems (crud in fuel tank, dry rotted tires, electrical probs (especially if it has been "rewired") and brakes can be issues.
If you want me to go with you to check it out send me a PM with contact info. You are only 30 miles away from me.