What's the worth of my 1990 Toyota longbed pickup in good condition

It all depends... Have you tried putting it online here to see what Caragurus recommends?

It sounds like you have a pretty nice vehicle and Toyota pickups always have a good market on them. I am not sure how others can throw out figures without more information like mileage, transmission (automatic or manual), drivetrain (2WD or 4WD), options, and overall condition for a 24 year old vehicle. Try the "Sell My Car" tool on CarGurus http://www.cargurus.com/Cars/sell-car/ and give as much information as you can. The values are generally spot on.