The reason we need pictures of the actual bike is that condition varies so wildly, and people's descriptions of bikes have little if any relevance on the actual condition. I've seen rusty junk described as "mint." I've seen bikes with obvious frame/fork damage for sale at full market value. Often bikes are crudely repainted which KILLS the value. Pictures tell the story.
You shouldn't invest $500 in this bike. But assuming the bike isn't wrecked you shouldn't need to. If the frame/fork/wheels are in good shape it might need $50-100 worth of parts, plus your labor. If it needs wheels or something big like a crankset, figure that into the price.