They usually go for between $5-30 depending on the condition and rareness.
Look each of them up on ebay to get an idea of what people are selling them for.
ebay is also probably the best place to sell them if it's worth it to you.
They look like HO model. We had them as kids in the 60's. I dont know the value. They ran in a track with 2 metal contacts. HO Slot Car Racing - HO Racing History