Read the Gen I Common Info and FAQ thread in its entirety.
Plan on:
Brake and clutch fluid flush and bleed
Rear end fluid change - check the rear wheel for splattering rear end fluid - look underneath the drive shaft at the weep hole for evidence of a leak. This would indicate your pumpkin seals are gone.
Coolant fluid change
Check fork seals for leaking - Plan to change fork fluid at a minimum.
Lubricate the pivot points on the shifter assy, rear brake pedal, center stand, and swing arm.
Probably needs new spark plugs
blow out the air filter - possibly replace
lubricate the worm gear on the wind screen motor (pull the auto-retract jumper while you are in there)
lubricate the drive shaft splines and the rear wheel - pumpkin splines
A few of the generation I FJRs have cam chain tensioner issues. When the motor is started, you might listen for a loose cam chain (right side of the motor). Worst case - a new CCT is about $80.00 and takes a couple of hours to change.
Even fewer of the gen I FJRs have a ticking noise that could be serious. There's a video on this on the Common Info thread.
Now - every bit of this can be done in your garage if you know the difference between a screwdriver and a wrench. Every item has a detailed pictorial on this forum showing you how to do this. You can accomplish all of this for about $50.00 in materials, a handful of tools (nothing special), and a full day in the garage.
I think the price is a fair asking price, but about $1,000.00 cheaper would be a steal. Anywhere in between is "reasonable".