A thing is worth what you're willing to pay for it. If the seller wants more, then no sale.
You can pretty well tell a $1500 car from a $3500 car. It's about the condition, and the remaining service life.
And those books are useless for cult cars. And heavily modified cars. Some mods don't help resale, no matter what, and others can help dramatically. You need to be on a forum like Pennocks to get a feel for the going rate.
Pacer Fieros are a special case, that no book can help with. There were only 2000 built to start with.